RES JUDICATA IN TAX MATTERS AND ITS LIMITS IN ON GOING RELATIONSHIPS

Abstract

This study analyzes the limits of res judicata in tax matters following the Brazilian Supreme Federal Court's (Supremo Tribunal Federal – STF) ruling on Theme 881. The Court held that, in continuing legal relationships, final and unappealable judicial decisions may lose their effectiveness following a subsequent declaration of the constitutionality or unconstitutionality of the applicable tax provision. This research is basic in nature, adopts a qualitative approach, and has an explanatory purpose, employing the hypothetical-deductive method and a bibliographic review. The study focuses particularly on the case of the Social Contribution on Net Profit (CSLL), in which the STF required the retroactive payment of the tax from 2007 onward, even for taxpayers protected by final judicial decisions. The findings demonstrate that the Court exceptionally relaxed the strict application of res judicata to preserve equality, free competition, and the uniformity of the tax system, seeking to balance legal certainty with tax fairness.