Many Conservatives, including Prime Minister Stephen Harper, oppose a Tory MP's motion to have Parliament re-examine the legal definition of when a fetus becomes a human being – a move critics decry as a backdoor attempt to reopen the issue of abortion.

Outside the Commons on Friday, a number of Conservatives said they will not stand in favour of the motion crafted by Kitchener MP Stephen Woodworth when it is put to a vote on Wednesday.

"I made a commitment to my community in the election campaign that I wouldn't support it," said Kathy McLeod, the MP for Kamloops-Thompson-Cariboo when cornered by reporters. "I perceive this as opening up the abortion debate and again, that's against my commitment."

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But there was a clear reticence on the part of Tory MPs who do not agree with Mr. Woodworth to publicly denounce the motion put forth by their caucus colleague.

And the three Conservative MPs who rose to debate the issue on Friday afternoon were all in agreement with Mr. Woodworth and his argument that human life begins well before a baby emerges from the birth canal.

"If Parliament, acting on behalf of all Canadians, refuses to even discuss the issue, it will be letting down the vast majority of Canadians who believe in honest and just laws, grounded in reality as we now understand it," said Stella Ambler, the Conservative MP for Mississauga South. "I also remind my colleagues that this is about fundamental, universal human rights and about a 400-year-old law, frozen in time."

David Anderson, the MP for Cypress Hills-Grasslands in Saskatchewan offered a similar argument.

"This is a very serious matter. If we presently have a law that decrees a certain human being is not a human being, is that an honest and acceptable law?" said Mr. Anderson. "Could such a law ever be considered just or legitimate? If Parliament finds itself in a situation where it allows one law that decrees the dehumanization and exclusion of an entire class of people, what are the safeguards that will prevent us from finding reasons to decree that others are not human beings as well?"

And March Warawa, the Conservative from Langley, B.C. said laws should be changed based on science, not rhetoric.

"Most parents are able to see their child's heartbeat and even see their child sucking their little thumb long before the moment of complete birth," said Mr. Warawa. "Why does Canadians law decree that such children are not human before the moment of complete birth?"

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The Liberals and the New Democrats each put up one speaker to say Mr. Woodworth's ultimate aim is to jeopardize access to abortion by granting legal protection to fetuses. The New Democrats, in particular, have spent time accusing the Conservative government of trying to reopen the abortion debate.

But even Mr. Woodworth concedes he does not have the support he needs to see his motion go forward.