The growth of e-commerce and marketplaces has transformed the dynamics of ICMS collection among the States. Interstate transactions destined for end consumers, previously taxed exclusively in the State of origin, began to also generate revenue for the State of destination. Constitutional Amendment 87/15 (CA 87/15) established the collection of the ICMS Rate Differential (DIFAL) on these transactions, in order to balance tax revenue among the federative entities – benefiting precisely the target audience of these transactions.

Since this was a model – set forth in art. 155, § 2, VII, of the Federal Constitution – that required the enactment of a complementary law (art. 146, I and III and 155, XII, “a”, “c”, “d” and “i”), the implementation of DIFAL gave rise to disputes between tax authorities and taxpayers, mainly regarding its applicability and temporal effectiveness.

Initially, the regulation was carried out through ICMS Agreement 93/15, issued in the same year as the Constitutional Amendment. Moreover, in an uncoordinated manner, several States enacted ordinary laws to establish the collection of this new form of DIFAL.

From this scenario, two actions reached the STF: ADI 5469, which challenged clauses of ICMS Agreement 93/15, and RE 1287019 (Theme 1.093), filed against a decision by the TJDFT (Federal District Court of Justice) which held that the regulation of DIFAL by complementary law was not necessary.

The actions were decided jointly and the vote of Justice Dias Toffoli prevailed. The understanding, based on art. 146, I and III, and art. 155, § 2, XII, of the Federal Constitution, was that CA 87/15 created a new tax-legal relationship between the sender of the goods or services and the State of destination. Therefore, the States and the Federal District could not collect DIFAL on interstate transactions with non-taxpayer end consumers without prior regulation by complementary law.

However, the Supreme Court modulated the effects of the decision so that the ruling would only take effect in the fiscal year following the conclusion of the judgment – that is, 2022, a year in which the legitimacy of the collection would be conditioned on the enactment of a complementary law.

In March 2021, less than a month after the judgment, Congress introduced PLP 32/21 to regulate DIFAL. However, due to lengthy debates, LC 190/22 - which sought to regulate ICMS-DIFAL - was only enacted on January 5, 2022.

LC 190/22, by amending the Kandir Law, created rules on DIFAL, addressing the active tax subject and the tax base. However, its art. 3 provided only for compliance with the 90-day waiting period (anterioridade nonagesimal) (art. 150, III, “c”, of the 1988 Federal Constitution), without mentioning the annual waiting period (anterioridade anual) (art. 150, III, “b”, of the 1988 Federal Constitution).

From then on, a new dispute over DIFAL in e-commerce transactions began. Since the STF had decided in Theme 1.093 and in ADI 5469/DF that CA 87/15 introduced a new tax-legal relationship in interstate transactions with non-taxpayer end consumers, compliance with the annual waiting period would also be required – which would allow DIFAL collection only from 2023 onward. Taxpayers expected the STF to maintain consistency with Theme 1.093 and uphold legal certainty regarding its own decisions, as required by arts. 926 and 927 of the Code of Civil Procedure (CPC).

This controversy gave rise to ADIs 7066/DF, 7070/DF and 7078/CE, which, among other points, challenged the constitutionality of art. 3 of LC 190/22 for not providing for compliance with the annual waiting period. The judgment was concluded at the Plenary Session of November 29, 2023. By a narrow majority (6x5), the vote of Justice Alexandre de Moraes prevailed: LC 190/22 had not established or increased a tax, but had merely set forth a new rule for the distribution of revenues. Therefore, only compliance with the 90-day waiting period would be required, as expressly provided for in art. 3 of LC 190/22.

The judgment of the ADIs broke with the logic of the understanding established in Theme 1.093, calling into question legal certainty and the trust of litigants in the decisions of the STF, the guardian of fundamental rights and guarantees.

In the judgment of RE 1426271 (Theme 1.266), under the rapporteurship of Justice Alexandre de Moraes, the STF established a binding precedent by majority and revisited the discussion on the annual waiting period. The Court confirmed that the vacatio legis corresponding to the 90-day waiting period provided for in art. 3 of LC 190/22 is constitutional.

As a second point of the binding precedent, the STF decided that state laws enacted after CA 87/15 and before LC 190/22 are valid. However, their effectiveness would be suspended and would only resume once LC 190/22 began to produce its effects.

Despite the taxpayers’ defeat on the annual waiting period argument and the attempt to invalidate state legislation enacted prior to LC 190/22, Justice Flávio Dino introduced a third point to the binding precedent to modulate the effects of the decision and, to some extent, reduce the impacts of the change in the understanding established in Theme 1.093.

In his modulation proposal, Justice Flávio Dino upheld the right – exclusively for the 2022 fiscal year – of non-payment of ICMS-DIFAL for taxpayers who filed lawsuits challenging the collection by November 29, 2023 – the date of the merits judgment of ADIs 7066/DF, 7070/DF and 7078/CE – and who had failed to pay the tax in 2022.

According to the Justice, the modulation was necessary to avoid retroactive fiscal surprise. Several taxpayers, upon noting the existence of decisions favorable to the annual waiting period argument, ceased collecting DIFAL in 2022. For these cases, collection would only be possible from 2023 onward.

The State of Ceará filed Motions for Clarification (Embargos de Declaração) against this third point, alleging obscurity in the expression “and who had failed to pay the tax.” According to the State, the modulation should not apply to (i) taxpayers who filed lawsuits but failed to pay the tax without any favorable court decision, nor (ii) to those who obtained a favorable decision conditioned on the deposit of the disputed amount.

However, in a virtual session concluded on March 13, 2026, the Plenary unanimously rejected the Motions for Clarification. The STF held that the modulation applies to taxpayers “who simply filed a lawsuit challenging the collection by the date of the ADI 7066 judgment (11/29/2023), regardless of whether they received a favorable preliminary decision, or whether they obtained one subject to a deposit.”

In his vote, the rapporteur Justice rejected the State of Ceará’s attempt to narrow the modulation of effects through the Motions for Clarification.

With this judgment, an important chapter of the DIFAL dispute in e-commerce transactions may be closing, at least regarding the validity of its collection by the States and the Federal District in 2022.

It is worth noting that there are other discussions regarding ICMS-DIFAL in the Judiciary, such as Repetitive Theme 1369, pending judgment by the STJ (Superior Court of Justice), which discusses whether LC 87/96 is sufficient to regulate ICMS-DIFAL collection involving taxpayer end consumers.

Since its establishment by CA 87/15, DIFAL has undergone a long path of legal debates involving legislative competence, waiting periods, and legal certainty. The STF’s decision in Theme 1.266 consolidated the understanding that LC 190/22 did not create or increase a tax, but merely regulated the distribution of revenues, requiring compliance only with the 90-day waiting period.

Although this position deserves criticism regarding legal certainty and legitimate expectations in the Judiciary’s decisions – in addition to representing a setback for taxpayers who advocated for the annual waiting period and the invalidity of state laws enacted prior to the complementary law –, the modulation promoted by Justice Flávio Dino sought to mitigate retroactive impacts. The measure preserved the legitimate expectations of taxpayers who sought judicial protection before the consolidation of the STF’s case law.

Machado Meyer’s tax team is available to clarify questions on this topic and the potential impacts of the modulation, depending on the particularities of each case.