The study from a newly created anti-corruption unit reportedly links the Mafia and criminal biker gangs to the construction industry, and the industry to political parties.
It says corrupt civil servants helped companies find loopholes that allowed the firms to increase the price tag on public-works contracts.
Then, it says a percentage of that extra money would occasionally be turned over to political parties as illegal donations.
Quebec's elections watchdog has already announced plans to probe deeper, saying the allegations represent a setback after 30 years of efforts to clean up political financing.
Radio-Canada and Montreal La Presse both reported on the contents of the study conducted by the provincial anti-corruption squad. The unit was created by the Charest government amid a plethora of scandals over the last two years.
Opposition parties have been demanding a public inquiry, but the government has stood its ground and insisted a massive police dragnet is the best way to handle the crisis.
Now these latest revelations have prompted renewed calls for a public inquiry.
La Presse quotes the document as saying that, even after two years of scandals, the level of corruption uncovered was on an "unexpected scale."
According to another quote from the document, the actual scope of corruption is so massive that it risks actually "usurping certain functions of the state."
Quebec Transport Minister Pierre Moreau expressed regret Thursday that the document had been leaked. He said the public release could tip off suspects to the fact that investigators are on to them.
"What matters to me, as a Quebecer, is that the bandits wind up behind bars," he told reporters in Montreal.
Moreau also tried to cut off demands for an inquiry.
He cited the report as proof that the government was on the right track and that it made a wise choice in appointing ex-Montreal police chief Jacques Duchesneau to head the unit.
"Our government gave Mr. Duchesneau the mandate (to examine this)," Moreau said.
"We had the courage to say, 'Let's examine this with the help of someone who is competent and trustworthy.'"
He also sought to defend the reputation of his department and of Quebec's civil service. He noted that the Transport Department has 6,000 employees — and that the vast majority are honest.
However, "there are rotten apples," he conceded.
"That's what the report seems to say."