MONTREAL- A public inquiry with possibly devastating political ramifications has begun in Montreal, with opening remarks from its chair Tuesday.

The Charbonneau commission will look into allegations of corruption involving construction firms, local and provincial governments, political parties, and even organized crime.

A recurring theme in recent allegations has been that elected officials benefited from kickbacks, raising questions about the financing of Quebec's political parties. There have also been allegations in news reports that Quebecers consistently overpay for public-works projects because of collusion scams.

In her opening remarks, commission president France Charbonneau made repeated attempts to stress that her inquiry will be free of government interference.

"The Quebec government created this commission of inquiry -- which is totally impartial and independent, well removed from any political considerations," she told a room crowded with journalists and inquiry staff.

"Nobody can tell [the inquiry] what to do, whom to interrogate or how to investigate."

She said her probe would be animated by the desire to denounce and correct the flaws in Quebec's public-procurement system. Part of its mandate includes interviewing experts and examining international practices.

Charbonneau explained that her inquiry cannot, under its mandate, examine agencies of the Government of Canada. But she pointed out that it can explore projects that received both provincial and federal funding.

She is expected to begin hearing witnesses in early June for three weeks before picking up again in mid-September.

Premier Jean Charest spent two years resisting demands for an inquiry, arguing that police probes and tougher laws were sufficient to deal with mounting evidence that the cost of public works was being driven up by criminal collusion involving organized crime.

He finally relented last year as public concern showed no sign of abating.

Charest backtracked after someone leaked a devastating report from former Montreal police chief Jacques Duchesneau, which had been intended only for internal government use.

Among its many allegations, the report for the province's anti-collusion task force had warned of disturbing links between organized crime groups like the Mafia with the worlds of politics and construction.

Charest relented again when people complained about the original terms of reference for the probe, which called largely for behind-closed-door hearings and set limits on Charbonneau's power. Her powers have since been expanded.

She explained Tuesday that the hearings will be as transparent as possible.

"Except for certain exceptions the hearings will be public. This is a fundamental principle of our legal tradition," Charbonneau said.

The commission must report by October 2013 -- right about the time Charest must call a provincial election.

There had been speculation Charest might hit the hustings before the inquiry. But with his party still struggling in the polls, and student unrest in Quebec, the premier has held off on an election call.

Quebec's elections monitor found in 2010 that an engineering firm made a series of illegal donations to the Quebec Liberals by using numerous employees to circumvent laws preventing corporations from contributing to political parties.

To a lesser extent both the Parti Quebecois and the now-defunct Action democratique du Quebec also benefited from similar illegal donations.

Even federal political parties may come under scrutiny. The governing Conservatives have also received many donations from players in the engineering firms implicated in construction-related controversies.

All these elements have Quebec journalists expecting a public inquiry that would rival, and perhaps even eclipse, Justice John Gomery's probe into the federal sponsorship scandal. So far more than 160 journalists have signed up to cover the hearings.

However, unlike Gomery, Charbonneau is not expected to grant media interviews during the inquiry. Gomery's remarks to reporters helped bolster a challenge against his partiality.

She asked journalists to refrain from interviewing witnesses until they had finished testifying. She said media interviews could hamper the inquiry.