Hundreds gathered in Montreal on Saturday to call on Quebec Premier Jean Charest to hold a public inquiry into the construction industry.
The protesters say a formal hearing would be the best way to root out corruption.
The Charest Liberals have been under intense pressure since a damning report was leaked to the media earlier this month.
The report says that construction companies, criminal groups and crooked civil servants conspired to drive up the price of public-works projects in Quebec.
The report says some of that money is then kicked over to political parties.
Parti Quebecois Leader Pauline Marois has repeatedly called for a public inquiry, but Mr. Charest says the matter is best left to police.
Jacques Duchesneau, a former Montreal police chief and the author of the report, is set to appear before a legislature committee in Quebec City on Tuesday.