About 60 officers with UPAC were deployed at four locations in Montreal and Sherbrooke to conduct the searches.
No one has been arrested, but investigators are looking for evidence to support suspicions about a $355-million water-meter contract signed in 2007, when former mayor Gérald Tremblay was in office.
The contract, which was awarded to consortium GÉNIeau, was cancelled two years later after costs ballooned and a report alleged there were irregularities with the tendering process.
Tony Accurso owned one of the businesses in the consortium.
On Tuesday, investigators targeted a Brossard business owned by Frank Catania, a man whose name and businesses have surfaced at the Charbonneau Commission.
Last week, searches were conducted at the Montreal offices of engineering-consulting firm BPR.
In spring 2014, members of the firm testified at the Charbonneau Commission about its alleged involvement in a water meter overbilling scheme. Three engineers with the firm pleaded guilty to charges related to their participation in that system.