New Liberal Leader Stephane Dion will face his first major caucus management test with Parliament's looming free vote on same-sex marriage.

Prime Minister Stephen Harper wants to hold a promised vote on whether Parliament should revisit the same-sex marriage bill passed last year by Parliament.

Debate would start Wednesday, with a vote likely on Thursday.

In Monday's question period, Harper tried to create some mischief for Dion by saying: "We promised Canadians a genuinely free vote on this issue in the House of Commons.

"I know the new leader of the opposition has said he will not allow a free vote of his caucus members. I hope that proves not to be the case, because the rights of members of Parliament are some of the most important rights we have."

In speaking with reporters afterward, Dion said while he will discuss the matter with his caucus, "It's respect of the Charter of Rights."

When Parliament last dealt with same-sex marriage, the bill passed 158-133, with 32 Liberals voting against it.

Then-Prime Minister Paul Martin required all cabinet ministers to vote for the bill. One minister, Joe Comuzzi, stepped down rather than vote for the bill.

On the weekend, MP John McKay essentially dared a new leader to kick him out of caucus for opposing same-sex marriage.

"I think it's probably unwise for any leader to 'whip' his or her caucus," McKay said Monday on CTV Newsnet's Mike Duffy Live, meaning compelling MPs to vote a certain way.

"The grievance of those who support the traditional definition of marriage is the previous two governments have whipped their cabinet, which means the vote in the House has been something less than entirely free."

Gerry Keddy, one of a handful of Conservative MPs who voted for same-sex marriage in 2005, agreed that whipping the vote has caused ongoing dissension.

A rights issue?

Michael Ignatieff, who finished second in the Liberal leadership fight, told reporters Monday, "It would be typical of Mr. Harper to use a Charter issue, an equality issue, to divide another party. That's the kind of thing that gives politics a bad name."

"To hear the argument that you don't pick your rights, well, in fact you do pick your rights," McKay said, noting the existence of the Charter's not-withstanding clause.

Same-sex marriage became framed as a rights issue when appeal courts across the country ruled that the traditional definition of marriage violated the equality rights of gays and lesbians under the Charter.

Bill C-38, the same-sex marriage law, brings the definition in compliance with the Charter.

While Harper has said he'd like to see the traditional definition restored, he's also said he wouldn't use the not-withstanding clause to do it.

Legal experts have said no government can restore the traditional definition of marriage without using the not-withstanding clause. That clause allows the government to uphold laws that would otherwise be declared unconstitutional.

Since Parliament passed C-38, more than 12,000 gay couples have married in Canada.

However, same-sex marriage opponents have argued that the Supreme Court didn't rule on whether the traditional definition was constitutional or not.

Legal experts counter by saying that the Supreme Court didn't reverse the appeal courts who said it was unconstitutional.

Social conservative activist Charles McVety promised Monday to have Christian activists hound any MP who had promised to protect the traditional definition but who voted against Wednesday's motion.

Laurie Arron, national co-ordinator of Canadians for Equal Marriage, argues that Canadians want to move on.

"This is the third vote in three parliaments under three prime ministers," he told The Canadian Press.

"It's quite clear that Canadians are sick and tired of this debate."

In a Dec. 3 Strategic Counsel poll for CTV and The Globe and Mail, 58 per cent of Canadians say they would vote to keep the same-sex marriage law, while 38 per cent would scrap it.

With a report from CTV's Rosemary Thompson and files from The Canadian Press