The Australian parliament is set to hold a vote on same-sex marriage, in which all MPs will be free to vote with their consciences.

According to the Sydney Morning Herald, the Liberal party, the senior partner in the ruling Liberal-National Coalition under Prime Minister Tony Abbot, is likely to suspend its binding position against gay marriage and allow MPs to vote freely, paving the way for parliament to take up the issue in its spring session. One Liberal MP said that it was “almost certain” that the whip will be lifted.

There have been two previous free votes in the Australian parliament on same-sex marriage and both were defeated.

Though the leader of the opposition Labour Party Bill Shorten is a strong supporter of same-sex marriage, a proposal calling for the whip to be applied on the issue was defeated at last week’s party conference. Members of the New South Wales branch of the Labour party have previously voted against same-sex marriage.

Prime Minister Tony Abbott, whose sister Christine Forster is in a same-sex relationship, promised before the election the Liberal Party would be free to decide on a conscience vote.

A Liberal MP, who would vote against same-sex marriage, said: ”I don’t think even Tony Abbott will stand up in the party room and argue against a conscience vote. It would appear to go against Liberal principles. I don’t think you would find any of my colleagues who would say a conscience vote was a bad idea.”

The matter is expected to reach a crucial stage in the next two sitting fortnights of Parliament in August and September after senior Liberals asked crossbench Senator David Leyonhjelm to introduce his draft bill to legalise same-sex marriage.

Senator Leyonhjelm said he wasn’t ”counting my chickens” on a vote for same-sex marriage on the floor of Parliament and a number of backbenchers said their ”gut feeling” was that it would be narrowly defeated even with a conscience vote.