Canadians whose loved ones died in the Sept. 11, 2001, attacks in the U.S. urged opposition MPs on Tuesday to support the renewal of two controversial anti-terror measures set to expire on Thursday.

"Canada should not be removing critical tools for fighting terrorism while terrorists are busy sharpening tools to use against Canadians and other innocent victims," Maureen Basnicki told reporters Tuesday from Parliament Hill.

Basnicki's husband, Ken, died in the World Trade Center after a hijacked plane slammed into the the North Tower of the New York City landmark. On Tuesday, she was joined by her daughter, Erica, in Ottawa to call on politicians to vote to "save these provisions and the Anti-Terrorism Act."

The House of Commons will vote Tuesday on whether to extend the two controversial measures in question, which provide special arrest and investigative powers.

The Liberals, who introduced the provisions in the chaotic aftermath of Sept. 11, 2001, now say it is time to roll them back.

The disputed Criminal Code measures — one allowing for investigative hearings of material witnesses and one that gives police the power to arrest and hold for 72 hours people suspected of being about to carry out a terrorist act — expire on March 1.

It is unlikely the numbers will work in favour of the Conservative government, which wants to see the laws granting the RCMP so-called "extraordinary powers" to continue for a three-year period. The NDP, the Bloc Québécois and the vast majority of Liberal MPs are poised to vote down the extension.

Liberals divided over issue

Liberal deputy leader Michael Ignatieff believes it is time to look past the measures, arguing the legislation had a built-in sunset for a reason.

"We are not prepared to take the prime minister at his word, as the leader has made clear from the beginning," Ignatieff said. "We sunset these clauses because it is the only way to fix this stuff, right?"

But differing opinions within the Liberal party have arisen over the issue, as some MPs are not ready to see the end of what they consider to be two key components of the Anti-Terrorism Act.

Former Liberal justice minister Irwin Cotler told the CBC the party was split between two lines of thinking. One position is that since the provisions have never needed to be implemented, they should therefore be sunsetted.

"Or you can take the position as I've taken," he said. "The fact that [the provisions] have not been used means that they have not been abused, but they may still be needed and therefore should be extended."

Liberal divisions over the issue have given Conservatives an opening to attack their opposition for being "soft on terrorism."

Harper offers compromise

Liberal MP Derek Lee said he isn't sure which way he'll vote, or what sanctions he may face if he goes against the party.

"I haven't actually been told how many whips are being brought out here," he said, chuckling.

Prime Minister Stephen Harper said the day before the vote he is open to suggestions for a compromise on new anti-terror legislation.

"The Senate has proposed a couple of things that are realistic; we want to see something. You know we are open to something, it is important to have anti-terror legislation that is effective," Harper said.

Still, the gesture has been dismissed as nothing more than a superficial offer of a compromise.

Liberal Leader Stéphane Dion has said that giving only 24 hours to submit a list of about 50 recommendations before the vote is a joke.

Ignatieff said it was too late and blasted Harper's compromise as "an 11th-hour response to what we've been saying all along."