SÃO PAULO, Brazil – Brazil's Supreme Court convicted former President Luiz Inacio Lula da Silva's three top aides, including chief of staff José Dirceu, of corruption on Tuesday.

In a landmark decision, the court found Dirceu, co-founder of the ruling Workers' Party, guilty of running a widespread cash-for-votes scheme known as Mensalão, according to Reuters. The party's president at the time, José Genoino, and its treasurer, Delubio Soares, were also convicted of corruption for taking part in the ploy, which paid politicians monthly installments of up to $10,000 for their votes in Congress. The three men face between two and 12 years in prison.

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Widely known as the biggest political corruption scandal in Brazil's recent history, the case has not been able to tarnish the reputation of Lula, who left office on Jan. 1, 2011, after two four-year terms, with an 87 percent approval rate, reported the Associated Press. The former president was not implicated in the case and does not face any charges, and a poll run by Datafolha said earlier this year that 57 percent of Brazilians would like him to return to the presidency in 2014.

According to BBC News, Dirceu has denied the scheme ever existed and said the allegations are political. A lengthy appeal process is also likely.

The top aides are just three among a total of 37 former ministers, politicians, businessmen and bankers on trial because of their involvement in Mensalão, reported Al Jazeera. Up to 30 of the defendants have already been found guilty since the trial began in early August.