The NDP has confirmed its plans to fight against the federal government's anti-terrorism bill, stating that Canada's security agencies don't need new powers.

After a caucus meeting, NDP Leader Thomas Mulcair said that, unlike the Liberal Party, his party will not be supporting Bill C-51. "We in the NDP are going to fight it," he said.

Mr. Mulcair said the legislation is overly sweeping and promises to be ineffective, stating the plan proposed by the government "goes too far."

Story continues below advertisement

He said that recent arrests in the Ottawa area on terrorism charges show the "current system works," adding that he is worried opposition against proposed economic projects could eventually be lumped in with terrorist activity.

The debate over the legislation begins Wednesday afternoon in the House.

The Liberal Party has already declared that it will side with the government on this bill, despite the lack of parliamentary oversight of the Canadian Security Intelligence Service.

The government announced its plans last month to boost the powers of Canada's spy agency, criminalize the promotion of terrorism and make it easier for police to make preventive arrests.

In Question Period on Tuesday, Prime Minister Stephen Harper rejected Mr. Mulcair's criticism of the bill's "broad" language before laying out the existence of judicial oversight over the new powers afforded to CSIS.

"We knew that with the NDP it would be only a matter of a couple of weeks before we got into this kind of conspiracy," Mr. Harper said. "Of course the reality is that under the legislation, based on information about imminent terrorist activity in Canada, should CSIS find it necessary to disrupt that, of course it would have to go to a court to get court sanction for those actions."

Two of the most important figures in the NDP – former leader Ed Broadbent and former Saskatchewan premier Roy Romanow – have written an open letter against Bill C-51. Party officials said the publication of the letter was part of the broader strategy to eventually vote against the proposal.