Process: 470/2015-T

Date: February 27, 2016

Tax Type: Selo

Source: Original CAAD Decision

Summary

This arbitral decision from CAAD (Process 470/2015-T) addresses the application of Stamp Tax under Item 28.1 of the General Stamp Tax Table (TGIS) to properties in vertical ownership. The claimant, representing an indivisible estate, challenged Stamp Tax assessments totaling €11,554.68 for 2014 on an urban property in Lisbon containing 12 independent units. The central dispute concerns whether the €1,000,000 threshold for Stamp Tax incidence applies to each independent unit separately or to the property's aggregate taxable value. The claimant argued that since no individual unit exceeded €1,000,000, the tax was illegally assessed, invoking constitutional grounds under Article 103(3) and principles of equality and proportionality. The claimant contended that treating vertical ownership differently from horizontal ownership (condominium regime) violates tax legality and constitutional principles. The Tax Authority raised a preliminary objection challenging the Arbitral Tribunal's jurisdiction, arguing that only assessment acts, not collection notes or installment payments, constitute appealable acts under the RJAT (Legal Regime of Tax Arbitration). On the merits, the AT defended that properties in vertical ownership constitute a single property under Article 2 of the IMI Code, distinguishing them from horizontal ownership where each autonomous unit is deemed separate. The AT maintained the assessment was lawful, resulting from direct application of legal provisions without discretionary elements, and that the total taxable patrimony value properly served as the tax base.

Full Decision

ARBITRAL DECISION

I. REPORT

  1. On July 24, 2015, A..., in his capacity as head of the Indivisible Estate of B..., NIF..., resident at Avenue..., no...., 1st left, Lisbon (hereinafter, Claimant), submitted a request for constitution of an arbitral tribunal, under the combined provisions of articles 2, no. 1, paragraph a), and 10, nos. 1, paragraph a), and 2, of Decree-Law no. 10/2011, of January 20, which approved the Legal Regime of Arbitration in Tax Matters, as amended by article 228 of Law no. 66-B/2012, of December 31 (hereinafter, abbreviated as RJAT), seeking the declaration of illegality and annulment of "tax assessment documents" nos. 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015... and 2015..., relating to the 1st installment and nos. 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015... and 2015..., relating to the 2nd installment of the Stamp Tax [Item 28.1 of the General Table of Stamp Tax (hereinafter, TGIS)], in the total amount of € 11,554.68, concerning the year 2014 and the urban property registered under article ... in the urban property register of the parish of..., municipality of Lisbon, included in the Indivisible Estate of B....

The Claimant attached 4 (four) documents and listed one witness, having made no request for the production of any other evidence.

The Respondent is AT – Tax and Customs Authority (hereinafter, Respondent or AT).

1.1. In substance and in brief summary, the Claimant alleged the following (which we mention mainly by transcription):

  • The aforementioned Stamp Tax assessments relate to the urban property located at Avenue..., no...., parish of..., Lisbon, registered in the respective urban property register under article ... and concern the tax period of the year 2014;

  • These same assessments were issued with the date of March 20, 2015, and the deadline for payment of the 1st installment expires at the end of April 2015 and the 2nd installment at the end of July 2015;

  • Given the provision of article 103, no. 3, of the Constitution (CRP), there is a manifest absence of one of the legal requirements of the taxable event in the assessments in question, which are affected by nullity, which is expressly invoked;

  • Subsidiarily, those Stamp Tax assessments are affected by error both as to the facts and as to the tax rate applicable;

  • The property in question is in vertical ownership and contains 12 parts, floors or divisions with independent use, of which a large part (but not all) is intended for housing, and none of the floors intended for housing has a taxable patrimony value equal to or exceeding € 1,000,000.00, therefore it must be concluded that the legal requirement for the incidence of the Stamp Tax provided in item 28.1 of the TGIS is not met, and therefore the challenged assessment acts are illegal;

  • The AT cannot consider the total value of the property for the incidence of this tax, as it constitutes flagrant illegality and unconstitutionality to consider in the calculation of the value the sum of the taxable patrimony values attributed to each floor or independent division;

  • The AT cannot distinguish between two situations (horizontal ownership and vertical ownership) where the legislator himself has not made such distinction, under penalty of violating the coherence of the tax system, as well as the principle of tax legality provided in article 103, no. 2, of the CRP and also the principles of justice, equality (articles 13 and 104, no. 3, of the CRP) and tax proportionality;

  • Item 28 of the TGIS, in allowing for differentiated taxation of the ownership of real estate property of equal value held by different persons based on criteria that may conflict, without the slightest justification, with, in particular, the principle of contributory capacity, cannot fail to be considered unconstitutional, for violation of the principle of equality;

  • The Claimant proceeded to pay the total tax amount contained in the assessments in question, therefore requests its reimbursement, plus indemnity interest, from the payment dates until its actual return.

  1. The request for constitution of an arbitral tribunal was accepted and automatically notified to the AT on August 7, 2015.

  2. The Claimant did not proceed to appoint an arbitrator, therefore, under the provision of no. 1 of article 6 and paragraph a) of no. 1 of article 11 of the RJAT, the President of the Deontological Council of CAAD designated the undersigned as arbitrator of the singular Arbitral Tribunal, who communicated acceptance of the assignment within the applicable period.

  3. On September 22, 2015, the parties were duly notified of this designation, and neither manifested the will to refuse the designation of the arbitrator, under the combined provisions of article 11, no. 1, paragraphs b) and c), of the RJAT and articles 6 and 7 of the Deontological Code of CAAD.

  4. Thus, in accordance with the provision of paragraph c) of no. 1 of article 11 of the RJAT, the singular Arbitral Tribunal was constituted on October 7, 2015.

  5. On November 4, 2015, the Respondent, duly notified for this purpose, presented its Answer in which, in addition to raising matters of exception, specifically impugned the arguments adduced by the Claimant and concluded in favor of the dismissal of the present action, with its consequent absolution from the claim.

The Respondent attached no documents, nor requested the production of any other evidence.

At the same occasion, the Respondent attached to the case file its respective administrative file (hereinafter, abbreviated as PA).

6.1. In substance and also in brief form, it is important to extract the most relevant arguments on which the Respondent based its Answer (which we mention mainly by transcription):

The Respondent begins by invoking the exception of incompetence of the Arbitral Tribunal ratione materiae, arguing as follows:

  • The Arbitral Tribunal is materially incompetent, in view of the provision of article 2 of the RJAT, to assess the legality of an installment of the assessment act, which is not in itself any tax act, there being no doubt whatsoever, including by the value of the case and all documents attached to it, that the Claimant impugns exclusively the collection notes which constitute the 1st and 2nd installments of the tax relating to the property;

  • Therefore, there is manifest material incompetence of the Arbitral Tribunal, and the exception invoked should be judged well-founded.

Subsequently, the Respondent enters into defense by impugnation, arguing as follows which we highlight here:

  • What is at issue here are assessments resulting from the direct application of the legal norm, which translates into objective elements, without any subjective or discretionary appreciation;

  • The concept of property is defined in article 2, no. 1, of the IMI Code, and it is provided in its no. 4 that, in the horizontal ownership regime, each autonomous unit is deemed to constitute a property, whereby it follows from the analysis of the normative provision that a "property in full ownership with floors or divisions capable of independent use" is, unequivocally, different from a property in the horizontal ownership regime, consisting of autonomous units, that is, several properties;

  • As regards the assessment of IMI, in the case of properties in full ownership, the taxable patrimony value that serves as the basis for its calculation will indisputably be the taxable patrimony value which the Claimant defines as "total value of the property";

  • Given that the assessment is correct and the tax calculated is due, indemnity interest is not due, first and foremost because there is no error attributable to the Services, which merely acted, as they should, in strict compliance with the legal norm;

  • The thesis defended by the Claimant lacks legal support, because although the assessment of Stamp Tax, in the situations provided for in item no. 28.1 of the TGIS, is carried out in accordance with the rules of the IMI Code, the truth is that the legislator reserves the aspects that require the necessary adaptations, namely those in which, as is the case with properties in full ownership, even though with floors or divisions capable of independent use (although the IMI is assessed in relation to each part capable of independent use) for purposes of Stamp Tax the property in its entirety is relevant, since the divisions capable of independent use are not deemed to be property, but only the autonomous units in the horizontal ownership regime, as provided in no. 4 of article 2 of the IMI Code;

  • The defect of violation of law by error as to the legal requirements should be judged unfounded, maintaining in the legal order the assessments impugned as they constitute a correct application of law to the facts;

  • It is not apparent how the taxation in question could have violated the principle of equality, since the provision of item 28.1 of the TGIS does not constitute any violation of this principle, with no discrimination existing in the taxation of properties constituted in horizontal ownership and properties in full ownership with floors or divisions capable of independent use, or between properties with residential use and properties with other uses;

  • Horizontal ownership and vertical ownership are differentiated legal institutions, and the legislator may subject to a distinct, and therefore discriminatory, tax legal framework properties in the horizontal and vertical ownership regime, particularly benefiting the more legally developed institute of horizontal ownership, without such discrimination having to be considered necessarily arbitrary;

  • One cannot conclude for an alleged discrimination in violation of the principle of equality when, in fact, we are faced with distinct realities, valued differently by the legislator;

  • In these terms, the collection notes of Stamp Tax, item 28 of the TGIS, 1st and 2nd installments, now impugned, remain entirely valid and legal.

  1. Notified for this purpose, the Claimant made pronouncements on the matter of exception alleged by the Respondent in its Answer, arguing in favor of the dismissal of the exception that was raised.

At the same occasion, the Claimant waived the examination of the witness listed by it.

  1. On November 18, 2015, a procedural order was issued dispensing with the holding of the meeting referred to in article 18 of the RJAT.

  2. Notified for this purpose, both Parties submitted written submissions, in which they reiterated the positions previously assumed in their respective pleadings.

II. PRELIMINARY EXAMINATION

The Arbitral Tribunal was regularly constituted.

The proceedings do not suffer from nullities.

The parties enjoy personality and judicial capacity, are properly represented, and are legitimate.

II.1. On the Incompetence of the Arbitral Tribunal ratione materiae

The Respondent raised this exception, invoking the following nuclear argument:

"The Arbitral Tribunal is materially incompetent, in view of the provision of article 2 of the RJAT, to assess the legality of an installment of the assessment act, which is not in itself any tax act, there being no doubt whatsoever, including by the value of the case and all documents attached to it, that the Claimant impugns exclusively the collection notes which constitute the 1st and 2nd installments of the tax [of Stamp Tax, concerning the year 2014,] relating to the property."

The Claimant made pronouncements on this exception, arguing in favor of its dismissal, in the following terms which are important to extract:

"Upon comparing the Claimant's application, it is verified that it requests the declaration of illegality of the tax acts relating to the assessment of Stamp Tax on item 28.1 of the General Table.

Obviously, the assessment of that stamp tax is subsequently embodied in the notification to the taxpayer for payment of the tax which in this case is divided into 3 installments, all of this reported to each of the floors of the building, since as many assessments are made as there are floors for housing existing on the property.

Even in point d) of its request, the claimant requests that 'the sums paid referring to the assessments (in the total amount of 17,331.83 € - corresponding to the 3 installments already paid) made relating to each of the floors or parts with independent use...' be reimbursed to her."

Given that the scope of material competence of the tribunal is of public order and its knowledge precedes that of any other matter (article 13 of the Code of Administrative Procedure applicable ex vi article 29, no. 1, paragraph c), of the RJAT) and that the infraction of the rules of competence ratione materiae determines the absolute incompetence of the tribunal, which is cognizable ex officio (article 16, nos. 1 and 2, of the Code of Civil Procedure applicable ex vi article 29, no. 1, paragraph a), of the RJAT), it is necessary to assess, primarily, the exception raised by the Respondent regarding the incompetence of the arbitral tribunal.

As a starting point for the assessment of this question, it is necessary to establish what is the object of this proceedings, as it was expressly outlined and delimited by the Claimant in the request for arbitral pronouncement. In this perspective, examining that initial pleading, it is important to highlight the following segments thereof:

"I – The object of the claim

The arbitral pronouncement has as its object the impugnation of the assessments contained in the Tax Assessment Documents nos. 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015 ... and 2015..., relating to the 1st installment and 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015..., 2015... and 2015..., relating to the 2nd installment concerning Stamp Tax of Item 28.1 TGIS"

"VII – Indication of the value of the economic interest of the claim

Value: corresponding to the sum of the values of the sums paid in the 1st and 2nd installments arising from the assessments in question, that is € 11,554.68."

"Value: € 11,554.68."

In light of these excerpts from the request for arbitral pronouncement, it appears abundantly clear that the Claimant expressly limited the object of these proceedings to the assessment of the claim for declaration of illegality of the 1st and 2nd installments of Stamp Tax (Item 28.1 of the TGIS), in the total amount of € 11,554.68, concerning the year 2014 and the referenced urban property. In fact, in stating the object of the proceedings and then developing its respective cause of action, the Claimant never alludes to the (total) assessment of Stamp Tax, made under item 28.1 of the TGIS, concerning the year 2014 and the referenced urban property (only mentions the 1st and 2nd installments), nor does it make any mention of the total value of the respective tax collection (only mentions the value of the 1st and 2nd installments).

That said, the competence of the tax arbitral tribunals established under the aegis of CAAD is, first and foremost, limited to the matters indicated in article 2, no. 1, of the RJAT, which provides as follows:

"1 - The competence of arbitral tribunals comprises the assessment of the following claims:

a) The declaration of illegality of tax assessment acts, self-assessment, withholding at source and payment on account acts;

b) The declaration of illegality of acts determining the taxable base when not giving rise to the assessment of any tax, acts determining taxable matter and acts fixing patrimony values."

In order to determine whether or not the Arbitral Tribunal is materially competent to assess the claim deduced in these proceedings, it is necessary to ascertain whether the request for declaration of illegality and consequent annulment of two of the installments of a Stamp Tax assessment, effected under item 28.1 of the TGIS, is equivalent to a request for total or partial annulment of such assessment or, if not equivalent, whether those installments, considered per se, could constitute acts susceptible to autonomous impugnation.

Regarding the first question, we advance from the outset that we understand that two installments of Stamp Tax do not equal an assessment of that tax. Whereas, no. 7 of article 23 of the Stamp Tax Code (CIS), as amended by article 3 of Law no. 55-A/2012, of October 29, provides that: "Where the tax is due for the situations provided for in item no. 28 of the General Table, the tax is assessed annually, in relation to each urban property, by the central services of the Tax and Customs Authority, applying, with the necessary adaptations, the rules contained in the IMI Code". Now, the expression "the tax is assessed annually" suggests that a single annual assessment is made, although it may be divided, for payment purposes – and only for this purpose – into installments, as follows from the provision of articles 44, no. 5 of the Stamp Tax Code and 120 of the IMI Code.

Thus, there are not as many assessments as there are installments in which the tax collection must be paid (contrary to the understanding evidenced by the Claimant by calling "assessment documents" each of the indicated Stamp Tax collection notes notified to it), since the division of an assessment into installments is merely a revenue collection technique. As stated in the arbitral decision issued in case no. 205/2013-T (available at www.caad.org.pt/tributario/decisoes), "from the circumstance that the value of the [Stamp Tax] assessment can be paid in several installments, it does not follow that there are three assessments (…) being, differently, one assessment that can be paid in several installments".

As explained by António Braz Teixeira (Principles of Tax Law, Volume I, 3rd edition, Coimbra, Almedina, 1995, pp. 243 and 244): "The payment corresponding to the tax obligation may be instantaneous or periodic (…) [being] necessary not to confuse the periodic payments which, although being realized by successive acts, at different moments, have origin in the same obligation and constitute the various portions of the same payment that was divided, with the payments that must be made periodically, not due to a division of the global payment, but rather to the periodic birth of new obligations, by the persistence of the factual requirements of taxation".

On the other hand, knowing whether a payment can be deemed as an autonomously impugnable part of the assessment refers us to the question of divisibility of the tax assessment act and consequent possibility of its partial annulment.

It has been understood, by doctrine and case law, that the assessment is a divisible act, both by nature, as it concerns a pecuniary obligation, and by legal definition, since article 100 of the General Tax Law (LGT) admits "total or partial success of administrative complaints or appeals, or judicial proceedings in favor of the taxpayer", a situation in which the tax administration is obliged "to the immediate and complete restitution of the situation that would exist if the illegality had not been committed, including the payment of indemnity interest, under the terms and conditions provided for by law". However, for there to be partial annulment of the tax act, it is necessary that the illegality affects it only in part (in this sense, the decision of the Supreme Administrative Court, issued on April 10, 2013, in case no. 0298/12, available at www.dgsi.pt). Thus, in cases where the tax act is divisible, if partial annulment of a tax act is requested, the court may not, in principle, annul it entirely; if total annulment is requested and the act is only partially annullable, the request will be partially unfounded.

Regarding the assessment of Stamp Tax, as has been repeatedly stated in various decisions of arbitral tribunals established under the aegis of CAAD (in this sense, among others, the decisions issued in cases nos. 205/2013-T, 408/2014-T, 726/2014-T, 736/2014-T, 90/2015-T and 137/2015-T, available at www.caad.org.pt/tributario/decisoes), "the assessment of tax is only one and only it will constitute a harmful act, susceptible of being subject to a single impugnation, whereby, when the law provides for its payment in several installments, staggered over time, the annulment of the tax act will have consequences regarding all of them, ceasing the obligation to pay or imposing the obligation to restitute the amounts of tax already paid by the taxpayer, as well as the indemnification of the situation through the payment of compensatory interest, all at the charge of the Tax and Customs Authority.

What the law does not provide for, neither in arbitral proceedings nor in judicial proceedings for impugnation, is the claim for annulment of payment of isolated tax installments, since such effect will only result from the annulment of the tax assessment act which, as we have seen, consists in the quantification of the total amount to be paid and which is only and exclusively a single tax act." (arbitral decision issued in case no. 90/2015-T).

In this framework, the 1st and 2nd installments of Stamp Tax (embodied in the aforementioned collection notes), object of the present request for arbitral pronouncement, are not impugnable per se, since they do not constitute tax assessment acts (cf. articles 95 of the General Tax Law and 97, no. 1, of the Code of Civil Procedure applicable ex vi article 29, no. 1, paragraph a), of the RJAT), but only two of the installments in which payment of the Stamp Tax assessed can be made, that is, they constitute portions of a global payment, originating from the same obligation.

In another order of considerations, as stated in the arbitral decision issued in case no. 726/2014-T, the "fact that the declaration of illegality of acts determining the taxable base when not giving rise to the assessment of any tax, acts determining taxable matter and acts fixing patrimony values are included within the competence of arbitral tribunals, pursuant to article 2, no. 1, paragraph b), of the RJAT, and that the request for constitution of the arbitral tribunal, as to them, must be presented within 30 days from the date of their respective notification, pursuant to article 10, no. 1, paragraph b), of the RJAT, leads to the necessary conclusion that the acts of autonomous impugnation referred to in article 10, no. 1, paragraph a), of the RJAT, are the acts of assessment, self-assessment and payments on account, even though, as regards these, a gracious complaint or hierarchical appeal has been filed, expressly or tacitly dismissed.

Having excluded the possibility of a payment constituting a tax assessment act, even less can it be attributed the nature of self-assessment or payment on account."

In these terms, it is imperative to conclude that the 1st and 2nd installments of Stamp Tax (embodied in the aforementioned collection notes), object of the present request for arbitral pronouncement, are not included within the scope of article 2, no. 1, paragraph a), of the RJAT, since they do not constitute "tax assessment acts", nor do they embody the "acts susceptible to autonomous impugnation" referred to in article 10, no. 1, paragraph a), of the RJAT, whereby it is judged well-founded the exception of absolute incompetence of the Arbitral Tribunal, ratione materiae, to assess the claim formulated in these proceedings and, consequently, the Respondent is absolved from the instance (article 16, no. 1, of the Code of Civil Procedure and articles 99, no. 1, 576, no. 2 and 577, paragraph a), of the Civil Procedure Code, applicable ex vi article 29, no. 1, paragraphs a) and e), of the RJAT).

As a consequence of the success of the exception of material incompetence of the Arbitral Tribunal, knowledge of the merits of the case is rendered unnecessary (article 576, no. 2, of the Civil Procedure Code applicable ex vi article 29, no. 1, paragraph e), of the RJAT).

III. DECISION

Pursuant to the foregoing, this Arbitral Tribunal decides:

a) To judge well-founded the exception of absolute incompetence of the Arbitral Tribunal, ratione materiae, and, consequently, to absolve the Respondent from the instance.

b) To condemn the Claimant in the costs of the proceedings.

VALUE OF THE PROCEEDINGS

In accordance with the provision of articles 306, no. 2, of the Civil Procedure Code and 3, no. 2, of the Regulation of Costs in Tax Arbitration Proceedings, the value of the proceedings is fixed at € 11,554.68.

COSTS

Pursuant to article 22, no. 4, of the RJAT, the amount of costs is fixed at € 918.00 (nine hundred and eighteen euros), pursuant to Table I annexed to the Regulation of Costs in Tax Arbitration Proceedings, at the charge of the Claimant.

Lisbon, January 27, 2016.

The Arbitrator,

(Ricardo Rodrigues Pereira)

Frequently Asked Questions

Automatically Created

Is Stamp Tax (Verba 28.1 TGIS) applicable to properties in vertical ownership where no individual unit exceeds €1,000,000 in taxable value?
According to the Tax Authority's position in this case, Stamp Tax under Item 28.1 TGIS is applicable to properties in vertical ownership based on the aggregate taxable patrimony value of the entire property, not individual units. The AT argues that vertical ownership constitutes a single property under Article 2(1) of the IMI Code, distinct from horizontal ownership where each autonomous unit is considered separate. Therefore, if the total taxable value exceeds €1,000,000, Stamp Tax applies even when no individual unit reaches this threshold. The claimant contested this interpretation as unconstitutional, arguing it violates equality and proportionality principles by treating economically similar situations (vertical vs. horizontal ownership) differently without justification.
Can a taxpayer challenge Imposto do Selo liquidation acts before the CAAD Arbitral Tribunal under the RJAT?
The Tax Authority raised a preliminary exception of material incompetence, arguing that the CAAD Arbitral Tribunal lacks jurisdiction under Article 2 of the RJAT to review liquidation acts or collection notes. The AT contended that only substantive assessment acts (atos de liquidação), not installment payment documents, constitute appealable acts before tax arbitration. The Respondent argued that the documents challenged (identified as '1st installment' and '2nd installment' notes) were merely payment instruments rather than the underlying assessment acts themselves. This jurisdictional challenge goes to the core of what constitutes an 'impugnável' (appealable) act under the RJAT framework, with significant implications for taxpayer access to arbitration for Stamp Tax disputes.
What constitutes an appealable act (ato impugnável) for Stamp Tax purposes in Portuguese tax arbitration?
An appealable act (ato impugnável) for Stamp Tax purposes in Portuguese tax arbitration must constitute a substantive assessment act (ato de liquidação) under Article 2(1)(a) and Article 10 of the RJAT, not merely a collection instrument or installment payment notice. The distinction is critical: the actual tax assessment decision determining the tax liability is appealable, but subsequent payment documents implementing that assessment may not independently constitute appealable acts. In this case, the dispute centered on whether the documents challenged (labeled as 1st and 2nd installment notes) were substantive assessment acts or merely derivative payment instructions. This distinction affects whether the CAAD has material jurisdiction (competência material) to hear the challenge, as arbitral tribunals can only review acts expressly within their statutory scope.
How does the Portuguese Tax Authority assess Stamp Tax on buildings with multiple independent units designated for housing?
The Portuguese Tax Authority assesses Stamp Tax on buildings with multiple independent units based on the property's legal classification. For properties in vertical ownership (full ownership with independent divisions), the AT applies Item 28.1 TGIS to the aggregate taxable patrimony value of the entire property as registered. This differs from horizontal ownership (condominium regime) where Article 2(4) of the IMI Code deems each autonomous unit a separate property. The AT relies on Article 2(1) of the IMI Code, which defines 'property' differently depending on the ownership structure. For vertical ownership, there is one property with one taxable value (the sum of all parts), triggering Stamp Tax if this total exceeds €1,000,000. This methodology applies the tax rate to the consolidated value rather than treating each floor or division as an independent property for tax purposes.
What are the legal grounds for nullity of Stamp Tax assessments under Article 103(3) of the Portuguese Constitution?
The claimant invoked Article 103(3) of the Portuguese Constitution, which establishes that no tax may be levied or collected except under statutory authorization. The alleged legal grounds for nullity centered on the absence of a legal requirement for the taxable event (falta de um dos pressupostos legais do facto tributário). Specifically, the claimant argued that the Stamp Tax assessments lacked legal foundation because Item 28.1 TGIS requires property value exceeding €1,000,000, which no individual unit satisfied. The constitutional argument extended to violations of tax legality (Article 103(2) CRP), equality principles (Articles 13 and 104(3) CRP), and proportionality. The claimant contended that assessing Stamp Tax based on aggregate value for vertical ownership, while horizontal ownership would assess per unit, creates arbitrary discrimination without basis in contributory capacity, rendering the assessments unconstitutional and therefore null under constitutional tax law principles.