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Tax reform is opening a new front in tax litigation, and it began even before the new taxes were effectively imposed.

Several taxpayers have filed preventive writs of mandamus seeking to exclude the imminent inclusion of IBS and CBS from the tax base of ISS and ICMS, arguing, among other grounds, that such requirement is contrary to the rationale established by the Federal Supreme Court in the judgment of RE No. 574.706 (Theme 69), according to which ICMS does not form part of the tax base of PIS and COFINS because it does not constitute the taxpayer’s revenue.

Long before the discussion on the merits itself, which falls outside the grounds adopted in the judgment of Theme 69, one procedural issue deserves particular attention: when does the interest to sue arise in a preventive writ of mandamus?

The answer to this question is decisive in determining when a taxpayer may turn to the courts to prevent the practice of an act it considers unlawful.

This issue was addressed in one of the first precedents on the matter.

In Writ of Mandamus No. 5000460-09.2026.4.03.6130, filed to challenge the inclusion of IBS and CBS in the tax base of taxes currently in force, such as IPI, ICMS, ISS, IRPJ, CSLL, PIS and COFINS, the 1st Federal Court of Osasco dismissed the case without a decision on the merits for two independent reasons: “(1) absence of a wrongful act or concrete threat of harm; and (2) lack of jurisdiction of the Federal Courts to hear a significant portion of the claims.”

According to the 1st Federal Court of Osasco, technical guidance contained in administrative manuals, preparatory documents, public statements by authorities involved in implementing the reform, responses to tax inquiries and other acts aimed at operationalizing the new system would merely represent a “conjecture regarding possible future action by the Administration,” and would therefore be insufficient to characterize a wrongful act or a concrete threat to the taxpayer’s rights.

With due respect, the decision adopts an overly restrictive interpretation of the interest to sue in a preventive writ of mandamus.

The writ of mandamus is grounded in Article 5, item LXIX, of the Federal Constitution and regulated by Law No. 12,016/2009. Under the applicable legislation, this type of action is available whenever there is a violation or a well-founded fear of violation of a clear legal right by an unlawful or abusive act of a public authority.

The law itself, therefore, does not require that the unlawful act have already been committed. Nor does it make the admissibility of a preventive writ of mandamus conditional upon the existence of complete regulations governing the tax assessment or of an individualized administrative act addressed to the taxpayer.

What justifies preventive relief is precisely the existence of a well-founded fear that a particular act will be carried out.

The central question therefore arises: at what point does government action cease to represent a mere future possibility and become a legally relevant threat?

In the dispute concerning the inclusion of IBS and CBS in the tax base of ISS and ICMS, the answer results from the combination of three factors.

The first is the silence of Complementary Law No. 214/2025, which does not expressly provide for the exclusion of IBS and CBS from the tax bases of ISS and ICMS. In fact, this is much more than mere silence.

Constitutional Amendment Proposal No. 45 of 2019 (PEC 45/19) provided for the exclusion of CBS and IBS from the tax bases of ICMS and ISS during the transition period of the tax reform. However, this provision was removed from the final wording of Constitutional Amendment No. 132/2023 and, consequently, from Complementary Law No. 214/2025.

The second factor is that, alongside this legislative silence, Tax Administrations have been issuing successive preparatory acts and official statements indicating, in a convergent manner, that these taxes will be included in the respective tax bases during the transition period.

In São Paulo, for example, the following have already accumulated:

(i) Adjustment SINIEF No. 24/2024;

(ii) Technical Note No. 2025.002-RTC;

(iii) the guidance contained in the SPED ICMS/IPI Frequently Asked Questions Manual;

(iv) public statements by tax authorities responsible for implementing the reform; and

(v) responses to tax inquiries issued by the São Paulo tax administration, expressly stating that IBS and CBS will be included in the ICMS tax base during the transition period.

It is possible that none of these acts, considered individually, would be sufficient to establish the well-founded fear required by Law No. 12,016/2009.

However, when examined as a whole, they reveal uniform, coordinated and repeated administrative action, demonstrating that the Tax Administration has already defined the interpretation it intends to adopt when the collection of IBS and CBS begins.

The mistake lies in confusing the moment when the economic effects of the act will materialize with the moment when the threat to the taxpayer’s rights arises.

Although collection will only begin in 2027, the administrative position seeking to include IBS and CBS in the tax bases of ISS and ICMS has already been expressed through various official instruments.

The threat, therefore, is present.

What remains in the future are only the financial effects of this administrative action.

This understanding is also consistent with the position consolidated by the Superior Court of Justice, according to which a preventive writ of mandamus requires an objective demonstration of the likelihood that the allegedly unlawful act will be carried out, and preparatory acts or concrete manifestations of administrative activity capable of evidencing future action by the Tax Authorities are sufficient.

This is not, therefore, a mere conjecture regarding the future conduct of the Public Administration. On the contrary.

The Tax Administration has already declared, through various official channels, which interpretation it intends to adopt when collection of IBS and CBS begins.

It also cannot be overlooked that several aspects of the new tax system are still subject to regulation, such as the establishment of definitive rates and certain operational procedures for tax collection.

These circumstances, however, do not eliminate the procedural interest.

The purpose of the preventive writ of mandamus is not to discuss the operationalization of the collection of IBS or CBS, nor their rates. The issue is a different one.

The objective is to prevent these taxes from being considered part of the tax base of ISS and ICMS when their collection begins.

This scenario is further reinforced by the ongoing consideration of Complementary Law Bill No. 16/2025, which proposes the express exclusion of IBS and CBS from the tax bases of ISS, ICMS and IPI, based on the principles of tax neutrality and transparency.

Regardless of the bill’s ultimate outcome, its existence demonstrates that the dispute has already been identified by the legislature itself, dispelling the notion that it is merely speculation constructed by taxpayers.

The conclusion reached by the 1st Federal Court of Osasco therefore warrants consideration.

Requiring an individualized administrative act or the actual assessment and collection of the tax in order to recognize the interest to sue excessively restricts the preventive function of the writ of mandamus.

The procedural interest does not arise with the first tax assessment or collection. It arises when government action, expressed through successive preparatory acts, institutional statements and converging administrative guidance, makes the practice of the allegedly unlawful act objectively foreseeable.

A different interpretation would undermine the very constitutional purpose of the preventive writ of mandamus.

If taxpayers were required to wait for the final regulations or the first tax assessment before turning to the courts, preventive relief would lose its purpose and would, in practice, become merely a remedial instrument.

The real issue, therefore, is not whether IBS and CBS are already being collected, but whether the Tax Administration has already expressed, in a sufficiently objective manner, the interpretation it intends to adopt when such collection begins.

When preparatory regulatory acts, responses to tax inquiries, operational manuals and institutional statements converge toward the same administrative position, the well-founded fear ceases to be a mere possibility and becomes a concrete threat to the taxpayer’s rights.

It is precisely for this moment that the Federal Constitution provides for the preventive writ of mandamus. Waiting for the harm to materialize would transform a preventive instrument into a mere reactive mechanism, undermining the preventive protection expressly guaranteed by the legal system.

 

References

[1] BRAZIL. Chamber of Deputies. Complementary Law Bill No. 16/2025 — excludes IBS and CBS from the tax bases of ICMS, ISS and IPI, amending the Kandir Law and Complementary Law No. 214/2025.

[2] CONFAZ — National Council for Fiscal Policy. Adjustment SINIEF No. 24, of December 6, 2024 — establishes standardized procedures for recording information relating to IBS, CBS and IS in electronic tax documents.

[3] National Electronic Invoice Portal. Technical Note No. 2025.002-RTC — adaptation of the NF-e and NFC-e layouts to the Consumption Tax Reform, with multiple versions published between March 28, 2025 and 2026.

[4] BRAZILIAN FEDERAL REVENUE SERVICE. SPED — Public Digital Bookkeeping System. Frequently Asked Questions Manual — EFD ICMS IPI, current version (item 19.1 specifically addresses the Tax Reform/IBS-CBS).

[5] SÃO PAULO (State). Department of Finance and Planning. Response to Tax Inquiry No. 32,303/2025.