MONTREAL - At least a half dozen construction union leaders are expected to face questions about possible Mob infiltration, extortion and intimidation on construction sites at upcoming Charbonneau Commission hearings, which kicked off Tuesday after a two-month summer hiatus.

Prosecutor Sonia LeBel made reference to such issues in a pre-session statement outlining the upcoming agenda for the commission, a line of inquiry that could open the door to testimony from such high-profile figures as alleged mobster Raynald Desjardins and construction magnate Tony Accurso.

The commission wants to know why crime figures such as Desjardins and Casper Ouimet of biker gang Hells Angels ran businesses funded by the FTQ solidarity fund.

“Unions hold a key role in construction, we have to see if they're vulnerable to infiltration by criminal gangs,” she said.

The commission, which has largely scrutinized misdeeds within the municipal level of government, exposing collusion among contractors and engineers, is also expected to further probe the provincial bureaucracy in the new session.

While the commission cost the careers of Montreal and Laval’s mayors, LeBel said it’s time to move on to another issue.

“Time is limited and that's why we can't follow every lead we get,” she said.

After LeBel's opening remarks, Marc-Andre Gelinas, who worked for the old Tecsult engineering consultancy firm, now called AECOM, took the stand and said that a cartel of firms rigged their bids for municipal contracts without the knowledge of the city of Gatineau.

The firms organized a system which would see them split up municipal contracts of between $25,000 to $500,000.

The system was set up in response to Bill 106, which put pressure on companies to compete for contracts.

Instead, the companies maintained their old rates and simply took turns making bids, in a system that lasted between 2003 and early 2009.

“There was never, to my knowledge, any bureaucrat or politician who was aware or a politician who was aware,” said Gelinas. “There was no way for them to tell because we were keeping our prices the same as before.”

Another Tecsult/AECOM engineer, Patrice Mathieu, testified  his company broke the law because Quebec City rules forced them to submit to calls for tenders which they felt were not financially viable.

“There was a shortage of contracts and competition was growing by the month,” he said.Mathieu's testimony continues Wednesday.

Federal politics, meanwhile, are entirely off-limits under the rules of the probe.

The closest the inquiry has come so far to scorching federal politicians has been in brief and peripheral references -- such as when engineering executive Rosaire Sauriol replied, "Yes," when asked whether he performed the same illegal fundraising activities at the federal level as he had provincially.

Chair France Charbonneau has been given extra time to complete her work. The corruption inquiry got an 18-month extension from the provincial government.

The inquiry will be required to submit a progress report by Jan. 31, 2014. Charbonneau must deliver her final report by April 2015.

-With a file from The Canadian Press