Justin Trudeau says opponents of abortion need not apply to run for the Liberal party in the next election.
And if they do apply, the Liberal leader says they'll be weeded out during the vetting process for nomination applications.
"As a party, we are steadfast in our belief ... that it is not for any government to legislate what a woman chooses to do with her body, and that is the bottom line there," Trudeau said Wednesday.
"I have made it clear that future candidates need to be completely understanding that they will be expected to vote pro-choice on any bills."
Exceptions will be made, however, for incumbent opponents of abortion who became MPs before the party officially adopted a pro-choice stance, such as Toronto MPs John McKay and Judy Sgro.
Their beliefs will be "respected to a certain extent," Trudeau said, "but our position as a party is we do not reopen that debate."
Trudeau revealed the party's new hard line on abortion one day before the annual "March for Life," in which thousands of abortion opponents are expected to descend on Parliament Hill.
In the past, Liberal MPs have been among those who've addressed the March for Life crowds. Opponents of abortion have traditionally formed a strong, vocal minority in the Liberal caucus, although their ranks have thinned considerably over the last two elections as the caucus shrank overall.
Until two years ago, Liberals did not have a party position on abortion, considering it a matter of conscience that should be left to each individual.
However, at their 2012 national convention, delegates for the first time approved a resolution that explicitly endorsed a woman's right to choose whether to have an abortion — adopting the same position long held by the NDP.
Trudeau said the evolution of the party position was cemented last year when Liberals "chose a resolutely pro-choice leader with over 80 per cent of the support of militants, of membership."
Abortion is just one issue on which would-be candidates' views are vetted during the party's so-called green light process for nomination applicants. Their views on same-sex marriage and the Charter of Rights are among the other issues canvassed, Trudeau said.
"We make sure that the people who are stepping forward are consistent with the Liberal party as it is now, as it stands under my leadership and under the feedback we're getting from Canadians across the country."
Trudeau's decision to bar abortion opponents from seeking Liberal nominations brings the party full circle from 1992, when party members gave then-leader Jean Chretien the power to appoint candidates.
That power was deemed necessary to thwart a group that called itself "Liberals for Life." They had taken over a number of Liberal riding associations where they hoped to elect staunch opponents of abortion to carry the party banner in the 1993 election.
Over time, Chretien used the power for a variety of purposes, including to protect incumbents, appoint star recruits and increase the percentage of female candidates.
For his part, Trudeau has said he won't use his power to appoint candidates, promising to allow open, democratic nomination contests in every riding. But he's using the vetting process for nomination applicants to weed out abortion opponents and others considered unsuitable.
Trudeau was initially stumped Wednesday when asked whether he'd allow Liberal MPs such as McKay to vote freely should an abortion bill come before the House of Commons.
"Well, it's a tough one because one of the things that's a strength of the Liberal party is that we draw in voices from right across the country and on a range of perspectives," he said.
Eventually, he added: "We will see what happens ... when that issue comes up. My preference is that we not be engaging in a discussion of abortion. For me, it's a debate that has been settled for the vast majority of Canadians and we don't need to reopen that issue."
For his part, McKay predicted he'll have few problems being one of only a tiny handful of anti-abortion MPs in an officially pro-choice party and caucus.
"Every MP has some points of estrangement between he and his party or she and her party," he said in an interview.
"I dare say I'll have a few awkward moments. That's life."
Indeed, he predicted it will be less awkward for him than for the vocal abortion opponents who make up roughly one-third of the Conservative caucus.
While the Conservative party hasn't barred abortion opponents from being candidates, "what's it got them?" McKay questioned.
Prime Minister Stephen Harper has pledged not to re-open the abortion issue and has intervened to shut down attempts by his backbenchers to introduce private members' bills on the issue.
Trudeau's hard line on abortion would appear to squelch the comeback hopes of some former MPs, such as Dan McTeague, who are staunch opponents of abortion.
Under the leader's dictum, the party won't give McTeague the green light to run for a nomination in his old Ontario riding.
McTeague could not be reached for comment.
NDP Leader Tom Mulcair said he doesn't understand how the Liberal party can have a "two-tier" approach to abortion, one position for incumbent MPs, another for all other would-be candidates.
"You're making an offer to the Canadian public. You're saying this is what we stand for," Mulcair said.
"The NDP has been clear on this. We know who we are. ... No NDP MP and no one running to be an NDP MP will ever vote against a woman's right to choose, simple as that."
Follow @jmbryden on Twitter