Conservative Leader Stephen Harper reopened the hot-button issue of same-sex unions on his first day on the federal election trail Tuesday, saying he would hold a free vote on changing the definition of marriage if he becomes prime minister.

Harper made the remark after Prime Minister Paul Martin announced Canadians will go to the polls on Jan. 23.

Harper, who has long promised that if elected he would hold a free vote on marriage, raised the issue himself during a news conference Tuesday in Ottawa.

Stephen Harper

"We were committed at the time of the convention and through the last debate to put a free vote to the next Parliament on this issue," he said. "It will be a genuinely free vote when I am prime minister. I will not whip our cabinet. Cabinet can vote as they want."

He said if the House votes against changing the law to allow same-sex marriages, the matter would be settled.

Harper, who believes same-sex couples should be recognized through civil unions, promised to preserve the gay marriages already performed across Canada.

Some observers say the Tory stance against gay weddings cost the party crucial support in urban Ontario and among younger voters.

But Harper may have raised the issue to pre-empt his critics, who say he's intolerant and has a secret agenda.