MONTREAL - A series of police raids in a town outside Montreal was billed Tuesday as the start of a crackdown in a massive Quebec corruption scandal.

They were the first strike by a provincial police unit created to deal with a mushrooming controversy that allegedly involves construction companies, politicians, and the Italian Mafia.

A police source described the raids in suburban Boisbriand, Que., as the first phase of Operation Hammer, announced in October in the midst of a controversy that has taken its toll on politicians at various levels.

The source said Tuesday's search warrants involved allegations of election-fixing, municipal corruption, defrauding the government, and buying or selling a contract.

Police searched Boisbriand city hall, the municipal public-works department, and a local construction company.

Boisbriand became embroiled in a wider corruption controversy when, in October, the CBC's French service reported on the murky relationship between elected officials and a company that controlled more than half the city's construction contracts.

The CBC cited evidence -- including a taped phone conversation -- that an industry player was urging municipal election candidates to quit that the former mayor could run unopposed.

In the end, former Mayor Sylvie St-Jean was defeated last month by challenger Marlene Cordato. The new mayor said she's co-operating fully with authorities.

"The contract we have with our citizens is to do our mandate and do our work in all transparency and with a lot of ethics," Cordato said in an interview.

"We have offered all of our collaboration to the Surete du Quebec for their work (Tuesday) morning."

Cordato said about 10 police officers were involved in the raid at city hall. They were seeking documents and left with a few cases.

The Boisbriand scandal is one of many related cases of alleged impropriety sweeping Quebec.

A barrage of media reports has suggested construction companies worked together to drive up the price of public-works contracts, shared profits with the Mafia, and illegally funded political parties.

Companies that submitted cheaper bids, without the cartel's approval, were allegedly threatened.

The province then launched Operation Hammer -- a $26.8 million investigation involving provincial police, Crown prosecutors, the federal Competition Bureau and the Mounties -- in an effort to crack down on the alleged practice.

The allegations have surfaced at a particularly sensitive time. The federal and provincial governments are embarking on a multibilion-dollar stimulus spree that represents the most expensive infrastructure program in Canadian history.

That means alleged fraud in Quebec's construction industry has implications for taxpayers across the country.

Radio-Canada, the French CBC, reported this fall on an alleged scam involving 14 firms.

It cited a federal study that concluded a kilometre of road cost 37 per cent more to build in Quebec in 2008 than it did in the rest of the country.

One report alleged the Mob controlled 80 per cent of contracts doled out by Montreal and that it received a cut out of every deal.

The city has since issued a moratorium on building contracts while it creates a more transparent bidding process. The province has announced new tendering rules for public contracts worth more than $25,000.