Lawyers for former Brazilian President Luiz Inacio Lula da Silva say they have filed a petition at the U.N. Human Right Committee denouncing what they call a lack of impartiality and abuse of power by the judge investigating the mammoth corruption-kickback scandal at state-owned oil company Petrobras.

Besides Silva’s attorneys, the petition filed Thursday in Geneva was also signed by British lawyer Geoffrey Robertson, a human rights specialist.

From his office in London, Robertson told reporters in Sao Paulo during a conference call that the petition details alleged violations of the International Covenant on Civil and Political Rights by Judge Sergio Moro, who is leading the Petrobras investigation.