MONTREAL -- Quebec's corruption inquiry has resumed after a two-month summer break -- and in this fall session unions will be put under the microscope.

The probe has already rocked the province, uncovering illegal activity by political parties, construction companies, municipal bureaucrats, and links to the Mafia.

Commission counsel Sonia LeBel said today, as she opened the fall session, that unions hold "a key position in the industry."

She said she wants to examine the possible infiltration of unions, links to organized crime, ties between businesses and unions, and intimidation and extortion on construction sites.

LeBel said the commission will delve deeper into the construction industry's vulnerability to criminal infiltration.

The commission, which has focused heavily on municipal politics around Montreal, will spend more time examining other parts of the province.

The first witness of the session that began today was from the regional head of an engineering firm for the Outaouais region, near Ottawa and the Ontario border. Commission lawyers say the scams there differed from those described in Montreal and Laval.

So far the probe has heard from 80 witnesses, including mayors, city bureaucrats, and engineering executives.

During the fall session, the commission is also expected to delve into construction contracts involving Quebec's transportation ministry.

Very little has been discussed about provincial politics so far.

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.