The Liberal Party is ready to ignore "gaps" in Ottawa's anti-terrorism bill and vote in its favour, while the NDP plans to put up a fight and could still oppose the proposed legislation.

The two parties were united in opposition to Canada's combat mission in Iraq last year, but they are heading in different directions in regards to Bill C-51, known as the Anti-Terrorism Act (2015).

After a caucus meeting on Wednesday, Liberal Leader Justin Trudeau announced his party will support plans to beef up the powers of the Canadian Security Intelligence Service and the RCMP, and to criminalize the promotion of terrorism.

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Mr. Trudeau said his priority will be to "address the gaps" in the bill. In particular, the Liberals will push for parliamentary oversight of Canada's national security agencies, and try to add a sunset clause that would force Parliament to evaluate the legislation before it is periodically re-enacted.

Mr. Trudeau said the Liberal Party will be willing to compromise during the current session of Parliament, and then promise to amend the legislation in its next election platform.

"The current government can accept that Canadians want greater oversight and accountability, or it will give us the opportunity to offer that directly to Canadians in the upcoming election campaign," Mr. Trudeau said.

The NDP blasted the Liberals for giving a "blank cheque" to the Conservative government, which has clearly rejected calls to increase the oversight of Canada's national-security agencies.

The NDP says it's still studying the legislation, but a party official said a majority of MPs currently oppose the bill. A final position will be taken next week.

In an interview, NDP Leader Thomas Mulcair said he does not believe that a new balance between security and rights needs to be achieved. "This notion that somehow there has to be this massive tradeoff, I don't believe that," he said. "The whole purpose of fighting against terrorism is to make sure that people who want to take away our rights and freedoms aren't the ones who wind up winning."

Mr. Mulcair said it remains an open question whether the Conservative plans are necessary or are "more political than practical." He added Mr. Trudeau and the Liberals have lost any leverage with the Prime Minister in improving the legislation.

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"Once he has already guaranteed him of his support, what's the purpose of pushing for amendments? Nothing is going to happen," he said. "Canadians want an opposition that will do the job of standing up to Stephen Harper."

During Question Period, the Prime Minister rejected calls for increased oversight, stating the new CSIS powers will be subject to judicial approval. He confirmed his trust in the Security Intelligence Review Committee, stating the body has proven its efficiency.

"The oversight is strong. What we need to do is make sure our police and security agencies have the tools they need," Mr. Harper said.

He added that the critical issue is to "make sure we are not going after them but after terrorists and jihadists."

Mr. Trudeau said the government's assurances are lacking, given past scandals involving CSIS and the RCMP on national-security issues.

"I believe that when a government asks its citizens to give up even a small portion of their liberty, it is that government's highest responsibility to guarantee that its new powers will not be abused," Mr. Trudeau said. "It is not enough, especially after all that we have learned in the last 14 years, for a government to say, simply, 'Trust us.' That trust must be earned, it must be checked, and it must be renewed."