Revenue Minister Jean-Pierre Blackburn says "stringent" measures were taken after allegations of tax fraud surfaced. (Canadian Press/Ryan Remiorz)

Two managers at the Canada Revenue Agency have been arrested and two other workers suspended without pay in connection with a complex tax fraud scam allegedly worth $4.5 million, National Revenue Minister Jean-Pierre Blackburn confirmed Wednesday.

The managers, arrested by RCMP Tuesday, are suspended without pay, as are two other employees of the agency, while authorities investigate a setup that allegedly involves three Montreal construction companies owned by Antonio "Tony" Accurso, a prominent businessman.

The companies — Simard-Beaudry Construction Inc., Construction Louisbourg Ltée, and Hyprescon — are alleged to have "funneled close to $4.5 million to two dummy corporations that have no commercial viability and are part of a false invoicing scheme," Blackburn said.

The companies are believed to have used profits from the scheme to pay workers under the table, or for their own personal benefit, Blackburn explained.

"Tax fraud is a serious crime which leads to serious consequences," he added. "The agency has to take stringent measures to counter tax fraud."

The federal government "is committed to protecting the Canadian tax system and [taking]measures to undermine the black market economy," Blackburn said.

The two arrested workers held management positions at the revenue agency, and are accused of facilitating tax evasion, said Patrice Chouinard, Montreal director of tax services at Revenue Canada.

"They would have been involved in a scam to avoid paying taxes, used to shield these companies from any suspicion," Chouinard told reporters at a Montreal news conference.

Questions about possible charges were being referred to the RCMP.

The companies have been summoned to appear in Montreal court on April 22.

Accurso involved in water-meter contract

Canada Revenue's investigation is the latest in a string of allegations against Accurso this spring.

Montreal's city auditor is reviewing a controversial water-meter contract involving the entrepreneur.

A $356-million contract to install meters was awarded in 2007 to a consortium of businesses, including one owned by Accurso.

The contract's tender process came under fire because of Accurso's personal friendship with Frank Zampino, former president of Montreal's executive committee.

Zampino admitted he spent his holidays on a boat with Accurso because the two have known each other for decades — but he did not interfere with thewater-meter contract process.

The contract is considered by some critics to be overly expensive for services to be rendered over the next decade.

With files from the Canadian Press