Parliamentary wrangling over same-sex marriage could be settled Thursday with the expected failure of a motion on whether or not to reopen the issue.

The motion calls on the government to "introduce legislation to restore the traditional definition of marriage without affecting civil unions and while respecting existing same-sex marriages.''

But the majority of Liberals are expected to oppose the motion and both the Bloc and NDP are forcing their members to vote against it, meaning the motion has virtually no chance of passing.

Prime Minister Stephen Harper has said if the House votes against changing the motion, the matter would be settled.

During the election campaign, Harper promised to hold a free vote in the House of Commons on whether Parliament should revisit the issue.

Both Harper and Liberal Leader Stéphane Dion are allowing their MPs to vote freely.

"There will be a free vote to prove that an overwhelming majority of my MPs are not willing to vote with the government on this issue," Dion said before the debate on the issue Wednesday.

"We want that to be over … It will be the end of the story."

Same-sex marriage became legal in Canada last year when Parliament passed Bill C-38 in response to a series of court rulings that gays had the right to marry.

Thirty-two Liberals voted against C-38, while 95 voted for it. Only three Tory MPs supported it.

Now, some of those Liberals who oppose same-sex marriage will not vote for the motion because they see it as a political ploy by Harper.

Liberal MP Paul Szabo, one of the Liberals who voted against same-sex marriage last year, has called Harper's motion "hollow" because if it were to pass, it would not immediately strike down the right of gays to marry.

Most constitutional lawyers have said the only way the Tories could change the law would be to invoke the notwithstanding clause, something Harper has said he would not do.

Liberal MP Bill Graham said the government knows such legislation would never pass, so it is using this round-about procedure.

"[It's] a manoeuvre that takes us no where, it's not designed to. It is designed to divide the House, divide the members of the House and divide the Canadian population on an issue that has been settled."