NDP Leader Jagmeet Singh said today his party would not support a Conservative government led by Andrew Scheer in a minority Parliament scenario after October's federal election.

The statement by Singh on Thursday came after the Liberals circulated a video of the Conservative leader speaking out against same-sex marriage during a debate in the House of Commons nearly 15 years ago.

"The resurfacing of Andrew Scheer's disgusting prejudice against LGBTQI2S+ people and families is very painful for many Canadians," Singh said in his statement.

"This is exactly why, if Canadians deliver a minority government in October, I will not prop up Andrew Scheer and the Conservatives. We can't trust Mr. Scheer or his caucus to champion the fundamental rights of Canadians."

On Thursday, Public Safety Minister Ralph Goodale tweeted a video of a 2005 speech by Scheer in which he opposed the Civil Marriage Act, which legalized same-sex marriage in Canada later that year. The Liberals are pressing Scheer to attend the upcoming Ottawa Pride parade.

The Pride parade in the national capital takes place Sunday, just a week after Ottawa Mayor Jim Watson came out as openly gay after decades in public life.

A Conservative minority government needing the support of the NDP to survive in a minority Parliament is not an unlikely scenario.

The polls suggest both the Liberals and Conservatives likely would fall short of a majority if an election were held today and would need the support of another party to govern. In the current context, the NDP is the only party likely to win enough seats to hold the balance of power.

What Scheer said in 2005

"There is nothing more important to society than the raising of children, for its very survival requires it," Scheer said in his 2005 speech to the Commons, delivered about a year after he was elected as the Conservative MP for the Saskatchewan riding of Regina-Qu'Appelle for the first time.

"Homosexual unions are by nature contradictory to this," he continued.

"There is no complementarity of the sexes. Two members of the same sex may use their God-given free will to engage in acts, to co-habit and to own property together. They may commit themselves to monogamy. They may pledge to remain in a loving relationship for life.

"In that sense they have many of the collateral features of marriage, but they do not have its inherent feature, as they cannot commit to the natural procreation of children. They cannot therefore be married."

Most Conservative MPs voted against the gay marriage bill. So did a number of Liberal MPs — as the Conservatives pointed out today in their reply to the Liberals' attack.

Goodale himself voted in favour of legalizing same-sex marriage in 2005, but voted against a private member's motion calling for the recognition of same-sex spouses in 1995.

In 1999, Goodale voted in favour of a motion embracing the definition of marriage as a bond between one man and one woman, and saying that Parliament should do what it can to protect it.

The Conservatives, meanwhile, accused the Liberals of trying to distract Canadians from the SNC-Lavalin scandal.

"Andrew Scheer unequivocally supports equal LGBTQ rights, including same-sex marriage as defined in law," the Conservative Party said in a statement. "He has advocated in the House for marginalized LGBTQ communities around the world."

Scheer has softened his stance on same-sex marriage since the debates over the Civil Marriage Act.

He supported a move to erase the traditional definition of marriage from the Conservative Party of Canada's policy book at its 2016 convention, arguing Canadians already had their say in two elections where same-sex marriage was a major issue, and that it had been legal for more than a decade.

But the Conservative leader has declined to march in Pride parades.