OTTAWA - Julie Couillard, the woman at the centre of the scandal that cost Maxime Bernier his job as foreign affairs minister, is refusing to voluntarily testify before a parliamentary committee.

And that has opposition MPs on the Commons public safety and national security committee threatening to subpoena her. In a letter Monday to the committee clerk, Couillard's lawyer said it would be unfair to force her to testify as long as Bernier is refusing to appear and explain his role in the affair.

Harper's office has said that neither the prime minister nor any of his ministers or MPs will take part in the committee's investigation, which Conservatives say will turn into a partisan circus.

Bernier resigned from cabinet last month after admitting that he forgot classified documents at Couillard's home. The pair had recently ended a relationship.

The committee is looking into that, and related security questions. Opposition MPs are concerned that Couillard, who was associated with criminal bikers as late as 2006, may have been trying to infiltrate the government on behalf of organized crime.

Couillard's lawyer, Jean-C. Hebert, suggested his client may eventually face criminal charges - for unlawfully having official documents in her possession - and that any testimony she gave before the committee could imperil her chances of a fair trial.

"Lopsided treatment by the committee of the two main witnesses, Mr. Bernier and Ms. Couillard, would seriously distort the requirement for equality of all before the law," he wrote.

Hebert also said that Couillard "without being certain of it . . . nevertheless has reasonable grounds to believe that the RCMP is currently undertaking an investigation."

The government has steadfastly maintained that Bernier's relationship with Couillard is a private matter and that there is no security issue.

The Foreign Affairs Department is looking into how the security breach involving the documents occurred, but the government has dismissed calls for a broader police probe.

Apart from Bernier, Couillard briefly dated a top adviser to Public Works Minister Michael Fortier. Bernard Cote resigned last week after admitting he was involved with Couillard while she was lobbying his department for a land developer.

It has also been revealed that Couillard met with the head of the Canadian Air Transport Security Agency in 2004, while she was bidding on two airport security contracts.

While a member of Parliament cannot be subpoenaed by a committee to testify, Couillard can be, and the Bloc Quebecois and NDP are eager to take that route.

However, Liberal public safety critic Ujjal Dosanjh said he'd rather wait until the fall when there's time to compel Bernier and Fortier, as well as Couillard, to testify.

Dosanjh said MPs can be compelled to testify if a resolution is passed by committee and approved by the Commons. But with Parliament scheduled to break for the summer this week, he said there's not enough time to go through that process until the fall.

He denied that Liberals are simply looking for a way to revive the scandal in the autumn, when his party may finally be ready to force an election. Rather, Dosanjh said he's just trying to ensure equality of treatment.

"Why would you compel an ordinary Canadian when you can't compel the ministers? . . . I want to send her a subpoena at the same time I want to send a subpoena to Mr. Bernier at least."