Maxime Bernier arrives to be sworn in at Rideau Hall in August. He is accompanied by Julie Couillard, whose revelations about classified documents left at her home prompted Bernier to resign. (Paul Chiasson/Canadian Press)

Federal opposition leaders are calling for an inquiry, a police investigation or some sort of formal probe into the security breach that led Maxime Bernier to resign as foreign affairs minister.

Leaders have also suggested Bernier's ex-girlfriend's links to biker gang members, and the bid her company has made for a government contract, need to be examined.

"The prime minister must have [a] public inquiry," Liberal Leader Stéphane Dion demanded in the House of Commons on Tuesday.

The calls for answers come after Prime Minister Stephen Harper abruptly announced Bernier's resignation. On Monday, Harper said Bernier was stepping down because he committed a security error when he inadvertently left classified documents at the home of his ex-girlfriend, Julie Couillard, in April.

Couillard, who was once married to a member of Quebec's Rockers biker gang, had her lawyer return the documents to the federal government late Sunday, and Harper has said he doesn't believe national security was compromised.

'Why do you sit on your duffs and do nothing for five weeks?'

The Conservatives say the misplaced files were a combination of publicly available information and classified material related to preparations for the NATO summit in Bucharest in April, where Canada was looking to secure more troop commitments from its allies for the war in Afghanistan.

Liberal foreign affairs critic Bob Rae said there needs to be an investigation into how such important documents could go missing for five weeks and no one at Foreign Affairs noticed.

"Why did it take the government five weeks to discover the documents were missing and why did it take the government five weeks to ask a question either of [Bernier] or Madame Couillard?" Rae said Tuesday in the House.

"Why do you sit on your duffs and do nothing for five weeks?"

His party says a public inquiry or police investigation are the only ways to get answers, while the Bloc Québécois is calling for a parliamentary committee investigation and the NDP has suggested an RCMP probe is necessary.

Bloc public safety critic Serge Ménard believes Harper was likely alerted to Couillard's past long before learning of Bernier's mishandling of classified files.

"Unless the RCMP is completely incompetent, and I don't think they are, I mean, they must have told the Prime Minister's Office," he said. "It's in the nature of things: when you have somebody who has continuous relations for a number of years, and been around, she is filed, and she is a security risk."

Conservative House leader Peter Van Loan says no security risks were overlooked, and says Bernier admitted to his mistake by resigning.

But the Conservative government has said it is conducting its own internal investigation, through the Department of Foreign Affairs.

Former Canadian ambassador Paul Heinbecker, who advised Lloyd Axworthy on security issues when he was Liberal foreign affairs minister, said an internal inquiry might be best because witnesses will hesitate to discuss classified information in a public setting such as a parliamentary committee hearing.

"The question is a professional one: 'What's the amount of damage that's been done?'" Heinbecker told CBC News on Wednesday.

"The real issue, I think, was: 'Was there anything in those documents that was very sensitive and that could have prejudiced national security?' And, if so, 'Who saw them, if anybody?' "

NDP worries about Canada's international image

NDP Leader Jack Layton said he worries that the international community will lose confidence in Canada.

"It wouldn't surprise me if the other countries involved are asking for some assurances now that Canada has its act in order when it comes to the issue of secret documents affecting NATO," he said Tuesday.

He has told the Globe and Mail that the RCMP must take a broad look at the case, including all the allegations made by Couillard during a taped television interview that aired Monday night, a few hours after Bernier's resignation was announced. Harper's announcement appears to have been made in anticipation of the broadcast.

Couillard talked about the documents in the interview, and she also said Bernier knew about her past ties to Quebec biker gangs right from the beginning of their relationship in 2007. She said her home in Laval, Que., had been bugged and that a private security firm found evidence that an electronic listening device had been removed from her bed.

Couillard also touched on her ties to the biker world in interview.

Couillard lived with Gilles Giguère, a well-known Montreal crime figure, for three years beginning in 1993. He was gunned down in 1996 when he decided to become a police informer after being arrested with a cache of submachine-guns and marijuana.

Couillard insisted that Giguère was not a biker and only knew Bob Savard, who knew Hells Angels kingpin Maurice (Mom) Boucher.

In 1997, she began dating and later married Stéphane Sirois, who admitted to being an enforcer for the Rockers, a Hells Angels puppet club. He later turned informant and testified against a dozen of his former colleagues in a 2002 trial.

During the interview, Couillard acknowledged Sirois was a biker when she met him, but said he left the gang at her insistence. Couillard and Sirois divorced in 1999.

Quebec politicians worried about representation

Several Quebec politicians expressed concern about the province's standing in federal cabinet with Bernier's departure.

Federal Liberal MP Pablo Rodriguez said Quebec was already weak in cabinet and now the situation is more dire. "Quebecers are the big losers today, because we, Quebecers were not well-represented in cabinet," he said.

Quebec has less sway in cabinet, because Bernier was "probably one of the most influential, if not the most influential minister from Quebec in Harper's cabinet," said Action Démocratique du Québec leader Mario Dumont.

Dumont said he's pressing Harper to ensure Quebec is still heard in Ottawa. "My main concern at this point is that Mr. Harper be conscious of that, and he will make a real [cabinet] shuffle," he said. "Now, there is a temporary shuffle. But there will be a real change of positions of ministers, and I hope the weight of Quebec in cabinet will not be affected by this situation."

Federal cabinet now includes four ministers from Quebec: Canadian Heritage Minister Josée Verner, Transport Minister Lawrence Cannon, Labour Minister Jean-Pierre Blackburn, and Public Works Minister Michael Fortier.

Cabinet shuffle in the works

Bloc Québécois Gilles Duceppe, meanwhile, wants an investigation into yet another aspect of Couillard's life. He said Monday that many questions remain unanswered, including how "people with very strange pasts" can bid on government contracts for airport security.

Le Devoir reported Monday that Couillard's business specializes in "systems of high security technology" that include security-system installations and passenger security. The information was provided to Le Devoir by a former employee at Couillard's firm.

Couillard received documents regarding airport security, according to the report.

In the fallout of Bernier's resignation, International Trade Minister David Emerson and Heritage Minister Josée Verner have been appointed to pick up Bernier's cabinet responsibilities while the prime minister searches for a new foreign affairs minister.

More ministerial changes will come soon, the CBC's chief political correspondent Keith Boag said.

"It makes it almost certain that we'll have a bigger cabinet shuffle this summer as the prime minister has to figure out what dominoes to move around now that Mr. Bernier's not there," Boag said.