A week after it raided the home and offices of the mayor of Laval, Quebec's anti-corruption unit has descended on the city a second time, hitting at least six construction companies with search warrants.

About 70 officers with the Unité Permanente Anticorruption, or UPAC, began their latest raids before 7 a.m. in the suburban municipality just north of Montreal.

UPAC said it was targeting firms related to Quebec construction boss Tony Accurso, who is already facing a dozen criminal charges related to possible tax fraud as well as bribery in connection with municipal contracts. Accurso's companies Simard-Beaudry Construction and Louisbourg Construction were raided — for the second time in eight days.

Tony Accurso's construction companies were once again raided, this time by the province's anti-corruption unit as part of an apparent investigation into contracts doled out by the city of Laval. (CBC)

Another pair of firms that were searched Thursday are Nepcon Inc. and Mergad Construction, part of a conglomerate owned by Laval's prominent Mergl family. Nepcon filed for bankruptcy protection in January, citing more than $4 million in debts, including more than $70,000 owed to Simard-Beaudry.

A third targeted business, Poly Excavation, co-owns a real-estate company that used to count Laval Mayor Gilles Vaillancourt as one of its shareholders. Vaillancourt, who has been mayor since 1989, says he sold his interest in 2001.

There's another link between Poly Excavation, a sewer and water-main firm owned by the Lefrançois family, and the mayor: Until April, Micheline Lefrançois had a Miami-area condo around the corner from an apartment owned by Vaillancourt's wife.

Accurso's firms, Nepcon and Poly Excavation are among eight companies that were awarded the lion's share of Laval's infrastructure and road work contracts between 2001 and 2008. It is believed investigators are looking into the bidding process for those deals and trying to determine whether it was rigged in the same way that a former construction mogul has testified that it was in Montreal.

Plainclothes and uniformed officers conducting the raids carried away boxes of files and took pictures of the sites.

Staff who answered the phone at Poly Excavation said the company is not talking to the media and curtly hung up. No one answered calls at Nepcon.