The Conservative leadership race is heating up as the membership deadline looms, with Maxime Bernier now vowing to use the military to close the Canadian border to illegal asylum seekers.

Immigration has long provided a key dividing line between various leadership candidates, but the debate went up a notch Monday as Kevin O'Leary promised to enact legislation to prevent some asylum seekers from obtaining a refugee hearing in Canada.

Mr. O'Leary said the legislation would violate the Canadian Charter of Rights and Freedoms, but that he would invoke the Constitution's notwithstanding clause to override the Supreme Court's 1985 Singh decision, which said asylum seekers had the right to a government hearing.

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"If the U.S. won't agree to closing the loophole so that those crossing into Canada illegally are returned to the U.S. where they are entitled to a fair hearing before an independent court, then Canada must act on its own," Mr. O'Leary said.

Mr. Bernier responded that he would also be willing to invoke Section 33 of the Constitution, the notwithstanding clause. He added he would call in the army if the RCMP and the Canada Border Services Agency failed to add enough resources to ensure the "integrity of the border."

"If it takes too long to put that additional manpower in place, I will look at additional temporary measures – including deploying Canadian Forces in troubled border areas," Mr. Bernier said.

The duelling statements came one day before Tuesday night's deadline to buy a Conservative Party membership to be eligible vote in the May 27 leadership race.

According to the most recent federal numbers, the RCMP intercepted 1,134 asylum seekers outside of regular points of entry in January and February, mostly in Quebec, British Columbia and Manitoba. The numbers are on the rise, but federal officials have said they are still within historical trends.

However, a number of government critics, including various Conservative leadership candidates, are arguing that the situation will only get worse and that Canada is in fact allowing some asylum seekers to "jump the queue."

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Mr. O'Leary said the notwithstanding clause was put in the Constitution by former prime minister Pierre Trudeau, arguing the federal government needs to use the power to deal with the "extraordinary" situation.

"This solves the loophole problem by passing a law making it clear that anyone crossing into Canada illegally from the U.S. would be ineligible to make a refugee claim," Mr. O'Leary said.

Mr. Bernier also announced that he would use the notwithstanding clause, a feature of the Constitution that was regularly used by the Quebec government in the 1980s, but has never been invoked by Ottawa.

"As I have said from the beginning we must close all legal loopholes being used to sidestep the proper refugee process. If the use of the notwithstanding clause is required to close these loopholes, of course we will use it," Mr. Bernier said in a statement.

At a minimum, all refugee claimants on Canadian soil are entitled to an oral hearing and fair procedures, under the Supreme Court's 1985 Singh decision that established modern refugee rights in Canada.

Another leadership candidate, Kellie Leitch, has been running ads on various websites in the final days of the campaign to promote her plans to "screen immigrants for Canadian values." Ms. Leitch has shaken up the campaign with her promise to require all arriving immigrants, refugees and visitors to be grilled by federal officials.