STF lawsuit could alter composition of Brazilian Chamber of Deputies

A legal challenge filed by the Democratic Labour Party (PDT) at the Supreme Federal Court (STF) could significantly change the makeup of the Brazilian Chamber of Deputies and state legislatures following the 2026 elections. The lawsuit, known as Direct Action of Unconstitutionality (ADI) 8.036, questions the current method used to distribute electoral leftovers, specifically the "largest averages" rule and the "80/20" criteria.

Under current rules, a party must reach at least 80% of the electoral quotient, and a candidate must receive at least 20% of that quotient, to participate in the distribution of remaining seats. If the STF accepts the revision, projections suggest up to 36 seats in the Chamber of Deputies could change occupants, potentially replacing elected deputies with alternates.

In the state of Bahia, projections indicate that seven seats in the Legislative Assembly and six in the Chamber of Deputies could be affected. Parties such as MDB, PSOL, PSB, PSDB, PP, PSD, Republicanos, and PL could potentially benefit, while parties including PT, União Brasil, Avante, PV, and PDT could see a reduction in seats.