Allegations of corruption at the Montreal office of Canada Revenue Agency have led to investigations of auditors, as well as employee suspensions and terminations, CBC News has learned.

Nine employees at the agency have been suspended or fired following allegations that officials there helped at least one construction industry boss in Quebec evade taxes.

Sources inside the agency told CBC's French-language service Radio-Canada that the problem goes back more than a decade.

The investigation into the Montreal office began following a tip to the RCMP in 2007.

Allegations of payoffs

An informer told police that a construction businessman had been paying off a manager at the revenue agency, according to court documents. The informant said the manager was helping the company avoid taxes.

One source at the agency agreed to be interviewed by Radio-Canada about how that was done. His name is being withheld to protect his security, but his story was corroborated by other sources within the CRA.

He said the person at the agency who allegedly received money was a high-profile figure at the Montreal office.

After the 2007 tip, both the RCMP and the revenue agency launched probes that led to charges against Montreal construction firm B.T. Céramique Inc. and its owner, Frank Bruno.

He was accused of helping two other companies produce false bills — bills to help the largest construction companies in Quebec avoid millions of dollars in tax claims. The owner of those two other companies, Tony Accurso, pleaded guilty to tax fraud and was fined more than $4 million.

Tax fraud

Bruno pleaded guilty a few months ago to tax fraud involving nearly $2 million. According to CRA sources, insiders helped him avoid an audit for several years.

Other agency employees reported irregularities with the tax file years before the informant went to police, but no one investigated, the source told Radio-Canada.

"The case is disturbing because it took so long. It took years to be discovered, which is weird," said Messaoud Abda, a professor of anti-fraud at the University of Sherbrooke.

"The problem may be that we need a whistle-blowing mechanism, so we can guarantee protection for people inside," he said.

To date, no one at the Montreal revenue agency office or any former employee has been charged in connection with these allegations.