The Conservatives will introduce a controversial motion Wednesday to reopen the issue of same-sex marriage, following through on Prime Minister Stephen Harper's election promise to revisit the issue.

The motion, which is expected to be voted on Thursday, will call 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 motion is not expected to pass. And Harper has said if the House votes against changing the law to allow same-sex marriages, the matter would be settled.

Harper said his caucus and cabinet ministers will be allowed to vote freely on the issue. Liberal Leader Stephane Dion, who is against the motion, said it's an issue about Charter rights, but has not yet revealed whether he will force his caucus to vote against it.

However, he hinted he may allow his MPs to vote freely because the motion doesn’t immediately strike down the right of gays to marry.

"If we have a party vote, he'll say that I muzzled my MPs and that if I had let them vote freely the motion would have passed," Dion said of Harper.

But the vast majority of Liberals are against reopening the debate. The Bloc Quebecois and the NDP are forcing their MPs to vote against it, meaning the motion has almost no chance of succeeding in the minority Parliament.

As well, Tory cabinet ministers John Baird, Jim Prentice, Loyola Hearn and David Emerson are also expected to vote against the motion, along with a number of other Tory MPs.

Liberal MP Paul Szabo, one of the Liberals who voted against same sex marriage last year, called Harper's motion "hollow" and said he'll vote against it.

"If the motion were to pass it will do nothing other than say the government better go and work out a way to do something," he said.

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.

During the election campaign, Harper promised to hold a free vote in the House of Commons on whether Parliament should revisit the issue. Following the January 2006 election, Harper said the vote would be held this fall.

With files from the Canadian Press