Brazilian interim President Michel Temer has been implicated in a bribery scheme at the state oil company, Petrobras.
The allegations came from a former Petrobras executive, Sergio Machado, who has been giving plea bargain evidence to prosecutors.
He said Mr Temer, among others, had asked him for illegal campaign contributions for a political ally.
Michel Temer has denied all the allegations.
Reuters quoted his office as saying that he had always observed campaign finance laws.
Mr Machado, who is himself accused of corruption, said Mr Temer requested the donation of around $440,000 (£309,000) for his PMDB party’s candidate’s campaign in the mayoral elections in Sao Paulo in 2012.
He said the contribution was made by a construction company and masked as an official campaign donation.
The money originated from the kickback scheme involving contracts handed out by Petrobras, he added.
He said that at the time he had made it clear to Mr Temer that the funds requested would come from “illicit resources”.
According to the Folha de Sao Paulo newspaper, Mr Temer has denied asking for illegal contributions to his party’s electoral campaigns and has said he never found himself in an “inappropriate place” with Sergio Machado.
He took office a month ago after his party played a leading part in getting President Dilma Rousseff suspended to face an impeachment trial.
Since then he has lost two cabinet members over an alleged corruption cover-up related to the Petrobras scandal.