UPAC spokeswoman Anne-Frédérick Laurence wouldn't confirm the location of the search.
Laurence said people have been interviewed by investigators. No arrests have been made.
Last week, UPAC raided the home of the mayor of Lachine, Claude Dauphin, as well as three former municipal politicians: Francine Senecal, Sammy Forcillo and Cosmo Maciocia.
Lachine's municipal office was also targeted in those searches.
The investigation relates to a multi-million dollar water-meter contract awarded by the city to the private consortium GÉNIeau. It was cancelled in 2009 after a review found irregularities with the tendering process.
At the time, it was the biggest contract ever awarded by the city.