Charest's name has surfaced for the first time during testimony at Quebec's corruption inquiry.
A witness testified that a lobbyist handed Charest a $3,000 cheque that had been signed by a senior executive with a windmill company.
The allegation was made during earlier testimony by Louis-Pierre Lafortune, which had been under a publication ban until Wednesday.
Lafortune, a former vice-president of a crane company, has been accused of gangsterism.
He said in his testimony that a lobbyist gave the $3,000 cheque in 2008 to the Liberal riding association of Sherbrooke, which Charest represented at the time. The cheque was made out a few days before the general election in December 2008.
Couillard said he spoke to Charest on Wednesday and that his predecessor told him he never received any such cheque.
"After having seen the reports in the media, I spoke to Mr. Charest myself," said Couillard. "He denied he received anything of the sort from Mr. Lafortune or anyone else."
Couillard made the comment at a Liberal caucus meeting in Saint-Felicien, Que.
The cheque was signed by Jean-Robert Pronovost, a senior executive with AAER, a firm that builds windmills.
It was legal in 2008 for individuals to contribute up to $3,000 to political parties.
Lafortune had invested $200,000 in the company, which was set up in the site of a former Hyundai plant in Bromont, Que.
He said it was the lobbyist, whose name can't be revealed, who confirmed he gave the cheque to Charest.
In the end, the windmill company went bankrupt in 2010.
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