Peter MacKay had a simple, gruff reply when asked by reporters what the definition of terrorism will mean in the government's latest anti-terrorism bill, C-51.

"Look it up," the justice minister said as he walked past waiting journalists on Parliament Hill Wednesday.

On the weekend, MacKay was quick to dismiss a terrorist link to the foiled alleged plot to attack a public place in Halifax on Valentine's Day because it lacked a cultural component.

"What we know of these alleged plans for a mass attack against our friends and our neighbours in (Nova Scotia)," he said on Saturday, "is that the attack does not appear to have been culturally motivated — therefore not linked to terrorism."

Halifax Threat Foiled 20150214

Justice Minister Peter MacKay heads from a news conference about a foiled mass murder plan in Halifax Saturday. MacKay said a plot to carry out killings in a public place there was not linked to terrorism. (Andrew Vaughan/The Canadian Press)

The term "terrorism" isn't actually defined in C-51; instead, one has to look to the Criminal Code.

Sec 83.01 (1) (b) of the code speaks to motivation as what distinguishes terrorism from other violent attacks.

It says terrorism is: "An act or omission, in or outside Canada, that is committed (A) in whole or in part for a political, religious or ideological purpose, objective or cause, and (B) in whole or in part with the intention of intimidating the public, or a segment of the public, with regard to its security, including its economic security, or compelling a person, a government or a domestic or an international organization to do or to refrain from doing any act, whether the public or the person, government or organization is inside or outside Canada."

There has long been a debate over this definition. 

Justice hawks worry it makes prosecutions too complicated, while civil libertarians say the government has no business policing people's thoughts and should worry only about actions.

Fears of broad interpretation

NDP Leader Tom Mulcair is among those worried the definition could be applied too broadly and used to target organizations that disagree politically with the government of the day.

"Experts warn that broad measures in this bill could lump legal dissent together with terrorism," Mulcair said Wednesday when announcing his party would strongly oppose the bill.

When asked by reporters which part of the proposed law would allow this, Mulcair echoed MacKay.

"Well, look at the definition section — look what's in there," he said.

Bill C-51 aims to target and disrupt "activity that undermines the security of Canada," which it goes on to say includes (among other things), "interference" with the "economic or financial stability of Canada," "terrorism" and "interference with critical infrastructure."

Mulcair acknowledges the section goes on to say, "For greater clarity, (undermining the security of Canada) does not include lawful advocacy, protest, dissent and artistic expression."

But Mulcair says that's not good enough — he wants guarantees the government wouldn't use the vagueness in the definitions to target its political foes in the future.

"Mr. Harper and the Conservatives have intimidated the Liberals into supporting this deeply-flawed legislation. We in the NDP are going to fight it," Mulcair told reporters. "The truth is, we cannot protect our freedoms by sacrificing them."