New Democrat MPs are criticizing Immigration Minister Jason Kenney for his support of a motion to study when human life begins, a day before MPs will vote on the measure.

Kenney is one of the government's most prominent cabinet ministers and the only one to say publicly that he is in favour of studying the Criminal Code's definition of when life begins. He said Monday that he would vote in favour of Motion 312, put forward by Conservative MP Stephen Woodworth, to create a parliamentary committee to study the definition.

The vote is scheduled for tomorrow night.

NDP MP Niki Ashton, the party's critic on status of women, says she's concerned a cabinet minister has said he supports the motion, calling that support "in clear opposition" to Prime Minister Stephen Harper's longstanding position that no one wants to see the debate re-opened.

"Not only has the debate been opened through this private members motion coming forward, but ... a senior member of this government has clearly stated his support," Ashton said.

Conservative Party Whip Gordon O'Connor also spoke against the motion last spring, arguing the issue is closed and that it's a matter to be decided by a woman along with her doctor and family.

'I'll vote in favour of the motion'

Kenney, who is known to be close to Harper and a key part of the Conservatives' election success, says he respects the points of view of his colleagues and that the vote will be a free vote rather than a whipped vote — that is, the parties won't tell their MPs how to vote.

"I'll vote in favour of the motion and I respect all the points of view of all the ministers and all MPs. I think we can have respectful debates on questions like this, and like I said, the grand tradition of all parties in government is to permit free votes on questions of conscience," Kenney said Monday.

"I think the prime minister has decided to continue with the grand tradition of Parliament, by multiple governments of multiple parties, to allow free votes on questions like this, like we did with euthanasia, like the death penalty, on questions that concern human life...it's a tradition well-rooted in precedent. There's nothing new here."

Interim Liberal Leader Bob Rae says he's been sanguine about the motion from the beginning.

"I don't think anywhere close to 20, 30 per cent of the members of this House are going to vote in favour of Mr. Woodworth's motion. I don't think it's going to be even remotely close," Rae said.

Ashton and NDP MP Françoise Boivin also called for changes to how private members business is reviewed before it gets to the floor of Parliament. Private members business is the only opportunity for MPs to really push for something, Boivin said, "but it still should have some rules. There's things we should not be accepting."

Parliament has experts who review legislation before it's presented to the House or Senate to make sure it's not already in front of Parliament and that it's constitutional.

'Fundamental to women's rights'

Jurisprudence has shown abortion is a fundamental right and therefore not a question of conscience, she added.

"They can put words in [Justice] Bertha Wilson's [ruling] til they're blue in the face, but it's a fundamental right. There's no such thing as voting your conscience," Boivin said.

Rae says he'd like to know how one member can prevent another from bringing in a motion that isn't completely out of order.

"If you believe in the House of Commons and you believe in private motions, you believe that members have a right to bring these motions forward and that people will vote on them. I don't see why this seems to be so unusual," Rae said.

Ashton says Kenney should listen to Harper and O'Connor.

"The question here is why he is choosing to stand up in opposition to his government's wishes on a motion that is so fundamental to women's rights and to Canadians' rights," she said.

Woodworth says the definition is 400 years old and needs to be updated according to modern science. Critics say the study will in essence reopen the debate over putting limits on abortion.

Not all MPs would say how they plan to vote on the motion. Conservative MPs Leon Benoit, Dean Del Mastro, Brent Rathgeber and Maurice Vellacott say they will support it, although their caucus colleague Ted Menzies wouldn't say how he plans to vote.

NDP House Leader Nathan Cullen says his party's MPs will vote against it, but says they don't have to whip the vote.

Most Liberal MPs are expected to vote against the motion, although Scarborough-Guildwood, Ont., MP John McKay says he is in favour of it. Liberal MP Sean Casey said in a news release Tuesday that he is personally anti-abortion but his constituents want him to vote against Motion 312, so he will oppose it.

Green Party Leader Elizabeth May says she will vote against the motion.