He left the PP in 1980 and he joined the Brazilian Labour Party (PTB), which his grandfather helped to form in 1945.

In 2005, Jefferson became involved in a corruption scandal related to the Correios, the Brazilian postal administration.

Facing a congressional inquiry related to his actions, Jefferson retaliated by exposing a cash-for-votes scheme, where he claimed congressmen were paid monthly sums in exchange for votes supporting president Luiz Inácio Lula da Silva, in what became known as the Mensalão scandal.

The scandal included dozens of parliamentarians of the government's coalition and two government ministers, among others, resulting in the indictment of forty people by the Supreme Federal Tribunal, for their alleged role in one of the country's biggest corruption scandals in recent years.

[10] On 23 October, Jefferson threw grenades and exchanged gunfire against agents of the Federal Police of Brazil coming to take him to prison after his house arrest was revoked after he insulted and threatened Supreme Federal Court minister Cármen Lúcia.