Immigration Minister Jason Kenney's office pursued a formal complaint against a Toronto lawyer who suggested publicly that the Conservative politician played a role in the decision to let former media baron Conrad Black return to Canada.

This spring, a staffer in Mr. Kenney's office filed a grievance against Guidy Mamann with the Law Society of Upper Canada, proposing he be investigated for violating its code of conduct.

In an interview this week, Mr. Mamann said he felt Mr. Kenney's office was trying to shut him up by complaining to the law society.

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"I believe that this tactic of trying to intimidate an immigration critic into silence, by trying to get him sanctioned professionally, is an abuse of [Mr. Kenney's] office," the Toronto lawyer said.

Mr. Mamann revealed the complaint to The Globe and Mail.

The veteran immigration lawyer offered commentary to media outlets, including The Globe and Mail, following news in late April that Mr. Black had engineered his return to Canada, a country whose citizenship he renounced in pursuit of a British peerage.

Canadian immigration lawyers said at the time it was extraordinarily rare for the federal government to grant the right to reside in this country to convicted felons while they're still in a foreign prison.

At the time, Mr. Kenney insisted he had not lifted a finger to help Mr. Black, who managed to secure a temporary resident permit to live in Canada while still behind bars at a Florida prison after being convicted in the U.S. The government said it left the file to bureaucrats.

Mr. Mamann, however, told The Globe and Mail on May 1 that he felt it was unlikely the Conservative government had no role in the decision.

"The idea that the minister didn't wink or nod in favour of this thing is impossible to imagine," Mr. Mamann said in comments published at the time.

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Kasra Nejatian, a staffer in Mr. Kenney's office, specifically mentioned this quote in the May, 2012 complaint he filed with the Law Society of Upper Canada, a self-governing organization for Ontario lawyers.

Mr. Nejatian charged in his letter to the law society that Mr. Mamann was quoted in media "as implying corruption or malfeasance by our office in our dealing with matters related to Conrad Black."

The law society answered the complaint in July by saying it found insufficient evidence to warrant an investigation into Mr. Mamann. It closed the file.

A lawyer for the law society told the Kenney staffer in a reply letter, provided to The Globe by Mr. Mamann, that his allegations offered no evidence of "conduct unbecoming a barrister or solicitor."

The Ontario governing body also said it had to ensure Mr. Mamann's right to freedom of expression "is not overridden by what might be characterized as a minor regulatory contravention."

Speaking this week, Mr. Nejatian said Mr. Mamann's claim that there was political interference in Mr. Black's case is completely false. "He made this claim with zero evidence and various access to information records have shown his claim to be untrue," the Kenney aide said.

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"He should apologize for misleading Canadians. Mr. Mamann works for one of the larger immigration law firms in the country. He knows that thousands of temporary resident permits are granted each year by civil servants, without political interference," Mr. Nejatian said.

"My complaint against Mr. Mamann to the law society was about his professional conduct. Not about politics," he said.

"I have a fairly thick skin. I rarely complain about outrageous comments. But when a lawyer does something that I think violates the codes of conduct, I feel duty bound to report it."

Mr. Mamann said it's bad form to try to attack his livelihood. "I don't think that is very becoming of a minister ... he should understand his statements and policies are going to be questioned in the media."

The Toronto lawyer said he still finds it remarkable the minister says he had nothing to do with the Black decision.

He said it's "very difficult to believe" that Mr. Kenney had no say in the approval. "You would think the most high profile temporary residence permit would go to the highest echelons of the immigration department," he said.

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"I don't think that many other immigration lawyers will disagree with me," Mr. Mamann said.

When the news broke in April, however, Mr. Kenney distanced himself from the Black ruling, saying it was made by "highly trained" public servants rather than their Conservative political masters. Mr. Kenney told reporters that when he learned of the application in February, he instructed immigration officials to handle it themselves.