OTTAWA — Andrew Scheer is challenging Justin Trudeau to follow through on a threat to sue him over his assertion that the prime minister politically interfered with the criminal prosecution of Montreal engineering giant SNC-Lavalin.

"Canadians want this scandal to be investigated in a legal setting where Liberals do not control the proceedings."

"If Mr. Trudeau believes he has a case against me, I urge him to follow through on his threat immediately," Scheer said in a statement.

Scheer said he looks forward to Trudeau testifying under oath in open court.

He called the threatened lawsuit "an intimidation tactic" aimed at silencing the Conservatives, who have been demanding a thorough, independent investigation of the affair. It's the same kind of tactic Trudeau has employed to silence former attorney general Jody Wilson-Raybould, said Scheer.

"This is what Justin Trudeau does when you stand up to him. He threatens you."

Like Wilson-Raybould, Scheer added: "We will not back down. We will continue to do our jobs, hold him to account and get to the bottom of this."

Nothing illegal happened: Wilson-Raybould

Wilson-Raybould maintains she was inappropriately pressured last fall by the Prime Minister's Office to stop criminal proceedings against SNC-Lavalin on bribery charges related to contracts in Libya. She believes she was moved to Veterans Affairs in a mid-January cabinet shuffle as punishment for refusing to do so. She resigned from cabinet a month later.

While she has called the pressure improper, Wilson-Raybould has said she doesn't believe anything illegal occurred.

Last week, Trudeau expelled both Wilson-Raybould and fellow former cabinet minister Jane Philpott from the Liberal caucus. Philpott had resigned from cabinet in early March, citing a loss of confidence in the government's handling of the SNC-Lavalin case.

At issue in the threatened libel suit is a statement Scheer issued on March 29, in which he said documentation provided by Wilson-Raybould to the House of Commons justice committee _ including a surreptitiously recorded phone conversation with the clerk of the Privy Council, Michael Wernick — is "concrete evidence that proves Justin Trudeau led a campaign to politically interfere with SNC-Lavalin's criminal prosecution."

Your statement, in its entirety, is beyond the pale of fair debate and is libellous of my client personally and in the way of his occupation as prime minister.Julian Porter, lawyer

Porter called the statement "highly defamatory."

"The prime minister supports wide-ranging and vigorous political debate on matters of public policy," he said in his letter to Scheer. "However, your statement, in its entirety, is beyond the pale of fair debate and is libellous of my client personally and in the way of his occupation as prime minister."

Porter said it's "entirely false" to say Trudeau interfered in the SNC prosecution, which has not been halted, or that he personally directed Wilson-Raybould to "break the law" and "fired" her when she refused. It's also entirely false to suggest Trudeau was aware of Wilson-Raybould's concern that he was politically interfering in the SNC case but lied to Canadians about it, Porter said.

Scheer's statement that the affair amounts to "corruption on top of corruption on top of corruption" was meant to suggest that Trudeau "had engaged in dishonest and corrupt conduct that would contravene the Criminal Code," a crime deserving of up to 14 years in prison, Porter said. That too was "entirely false."

Scheer 'will not be intimidated': lawyer

In response, Scheer's lawyer, Peter Downard, wrote back Sunday that Scheer "will not be intimidated" and is simply performing his "constitutional duty" to hold the government to account.

If Trudeau is serious about suing, Downard said he must immediately take steps to preserve all relevant documents and to notify all members of his government, past and present, who've been involved in the SNC-Lavalin matter that they can expect to be called to testify.

If Trudeau does not proceed with the threatened lawsuit, Downard said Scheer will conclude that Trudeau "has properly acknowledged that Mr. Scheer's statements were appropriate and grounded in evidence before the Canadian people."

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