UPAC investigators were seen taking boxes from his home this morning.
Eight raids have been conducted in recent weeks in relation to a $355-million cancelled water-meter contract.
Last week, UPAC raided the home of the mayor of Lachine, Claude Dauphin, as well as three former municipal politicians: Francine Sénécal, 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 during Tremblay's tenure to the private consortium GÉNIeau. Tremblay cancelled the contract in 2009 after a review found irregularities with the tendering process.
Tremblay served as mayor of Montreal from 2002 until his resignation in 2012.