The vote in Parliament on whether to study when life begins shows a split in the Conservative caucus, opposition MPs charge.

Eight cabinet ministers, including Status of Women Minister Rona Ambrose, Immigration Minister Jason Kenney and International Co-operation Minister Julian Fantino, voted in favour of the motion by Conservative MP Stephen Woodworth.

The motion would have set up a parliamentary committee to study whether the Criminal Code's definition of a human being is out of date.

Most of the MPs who voted in favour of the motion — 87 — were from the Conservative caucus. Four Liberals voted in favour of it. The NDP, Bloc Québécois and Green Party Leader Elizabeth May all voted against the motion, which they charged would re-open the debate on setting limits on abortion.

Liberal MP Justin Trudeau says Ambrose was hypocritical as status of women minister to vote for a motion that could have resulted in women having fewer rights.

"Her responsibility is to women in this country. That's what you do when you become a minister. You're not just responsible to your constituents, you're not just responsible to your supporters or the people who vote for you, you're responsible to all Canadians on a file that touches all Canadians. She lacked leadership on that level," Trudeau told CBC News on Thursday.

"What we're beginning to see is that Mr. Harper's iron grip on his cabinet is loosening and the true colours of the Reform base are showing through."

Harper voted against study

The vote was a free vote, meaning MPs weren't told what position to take.

Prime Minister Stephen Harper made it known he would vote against the motion, and party whip Gordon O'Connor, under most circumstances responsible for ensuring MPs vote according to the party's wishes, gave a speech in the House of Commons explaining why he would vote against Woodworth's motion.

Many observers took that as a signal to MPs of how Harper wanted them to vote. He has repeatedly said the party isn't interested in debating limits on abortion.

"I think what it shows is to what extent inside the Conservative Party the view that women do not have the right to choose is very widespread. If you know the private opinions, or the opinions, of the members of the Conservative caucus, it's not stunning," Interim Liberal Leader Bob Rae said Wednesday night.

Fantino and his parliamentary secretary, Lois Brown, both voted in favour of the study, indicating the government isn't likely to reverse its policy not to fund abortions in developing countries. The policy was a source of controversy for the government in 2010 when Harper announced he would push G8 leaders to focus on funding maternal and child health in developing countries.

'Responsible for women's rights'

NDP Leader Tom Mulcair calls Ambrose's vote shocking, since she had told a parliamentary commission she had the opposite position.

"In fact, a person who's responsible for women's rights is in a very delicate position when she votes against a decision by the Supreme Court of Canada which upheld the rights of women," he said.

He stopped short of calling for her to resign.

Two women's groups in Quebec, however, demanded Ambrose step down from her cabinet post. The Fédération des femmes du Québec and the Fédération du Québec pour le planning des naissances said in a joint press release that someone in the status of women cabinet post was supposed to protect women's interests.

Immigration Minister Jason Kenny, left, and Agriculture Minister Gerry Ritz were among 87 Conservatives and four Liberals to vote in favour of Motion 312, backbench MP Stephen Woodworth's controversial motion to study the definition of a human being. (Fred Chartrand/Canadian Press)

Woodworth said Thursday that he plans to keep fighting for his beliefs. He says while it's unlikely he'll get another chance in this Parliament to present a private member's motion, he will support and advise other MPs who want to try their own motions or bills.

He defended Ambrose's right to vote as she chose on the motion.

"I think there are many women who would be offended at the notion that because they are a woman, their rights depend on dehumanizing and excluding another human being," he said.

"To say that Motion 312 has implications for women's reproductive rights is really to say that women's reproductive rights depend on the pretence that some human beings are not human beings."

'Full confidence' in Ambrose

Ambrose said on Twitter Wednesday night that she voted in favour of studying section 223, part of the homicide provisions of the Criminal Code, because of sex selective abortion.

"I have repeatedly raised concerns about discrimination of girls by sex selection abortion: no law needed, but we need awareness!" Ambrose tweeted.

She rose at the end of question period Thursday but didn't explain why she voted the way she did. Instead, she claimed that it was the first question she'd had on the status of women file this year.

"And you know why that is? Because this government has an incredible track record for standing up for Canadian women," she said. "We have increased funding for Status of Women to its highest point in Canadian history and so far in just a couple of years, we've funded over 550 projects from coast to coast to coast to tackle violence against women and empower women and girls and we'll continue to do just that."

Asked for more information about the claim, a spokeswoman for Ambrose said she had cautioned in her answer that she thought it was the first question. The spokeswoman couldn't provide a date for the last time Ambrose was asked about a status of women file.

Labour Minister Lisa Raitt, who voted against the motion, said Ambrose is a good minister.

"I have full confidence in Minister Ambrose's ability to serve the Canadian public in both of her capacities, as minister of public works and minister of the status of women," Raitt said.

"I believe that last night was a free vote. We did it as individuals. We did not do it as ministers."