Luiz Inacio Lula da Silva's former chief of staff denied corruption charges.
Jose Dirceu, once one of the president's closest confidants, was charged by Brazil's Supreme Court with corruption and conspiracy for allegedly masterminding a 2005 bribes-for-votes scheme.
"I have a clear conscience because I am innocent," Dirceu declared at a news conference. "There is no evidence to substantiate the charges levied against me. I have all the proof needed to rebut every accusation."
Dirceu was considered a top presidential prospect himself before allegations surfaced that he orchestrated the scheme to buy votes with monthly bribes of as much as US$13,000 (9,500 EUR). Stripped of his right to hold political office for eight years, he faces 15 years in prison if convicted.
Several other prominent former legislators, Cabinet ministers and officials of Silva's Workers' Party also face charges in the scandal - dubbed the "mensalao," or "big allowance."
The charges against members of Silva's inner circle have raised hopes among some Brazilians of an end to impunity for corrupt politicians.
In an unrelated case, Brazil's Senate ethics committee was considering Thursday whether to begin proceedings that could lead to the expulsion of Senate President Renan Calheiros, another close Silva ally, who has denied allegations that he accepted payoffs from a construction company.