Greens senator Sarah Hanson-Young. Credit:Andrew Meares Prime Minister Tony Abbott's sister, Christine Forster, said Liberal MPs needed to settle the issue in the second half of 2015 to prevent it from becoming a political football during an election year. This comes as estimates of parliamentary support now have the House of Representatives just two votes shy of a majority, after Labor MP Joel Fitzgibbon became the latest MP to reveal his support. The Senate is estimated to have a majority of one in support. Greens senator Sarah Hanson-Young already has a private member's bill to legalise same-sex marriage before Parliament. On Tuesday, she will announce the party will use its allotted Senate time on June 18 to start debate on the bill.

The tally of countries recognising same-sex marriage is rising. "Gay and lesbian Australians deserve better than being treated as second-class citizens; it's well and truly time the Parliament acted," Senator Hanson-Young said. "Cupid doesn't discriminate and neither should the law." The party has then nominated November 12 for a vote on the bill. This would be in the second last sitting week of the year. The Greens' move came as Liberal supporters of same-sex marriage were pressed on what the party would do in the wake of Ireland's referendum.

Ms Forster, a City of Sydney Councillor, said there were a number of triggers for bringing on a party-room debate. These included a bill before Parliament or an individual MP taking the initiative and raising it in the party room. "This is an issue that needs to be dealt with [during] the term of the Parliament," Ms Forster said. Liberal frontbencher Simon Birmingham said Liberal MPs would discuss a free vote at an "appropriate" time this year, but hosed down suggestions MPs could debate the issue as soon as Tuesday's meeting. Senator Birmingham noted that with Senate estimates hearings running for the next fortnight, many senators were called away on other business. Backbench MP and same-sex marriage supporter Warren Entsch told ABC 24 that he was looking to have "some sort of plan" to put to Mr Abbott in the "near future".

But he stressed that Liberal MPs in favour of same-sex marriage were not going to be "aggressive" about their support. "The last thing we want to do is create a whole lot of conflict." On Sunday, Mr Abbott left open the idea of a party-room discussion on same-sex marriage and a free vote. "If it comes before our Parliament again, our party room will deal with it. Our party room will decide whether our existing policy continues or not, and then we'll have a good debate," he said. While he is a firm backer of the existing definition of marriage, he described same-sex marriage as "obviously a serious issue, a very serious issue".

Senator Hanson-Young's bill is not the only one before Parliament. Liberal Democrat senator David Leyonhjelm​ introduced a "freedom to marry" bill last year. He planned to proceed to the debate stage of his bill in March to get Liberal MPs to decide their position on a free vote. But he pulled the session after Liberal MPs passed up the opportunity to raise it in the relevant party-room meeting. Follow us on Twitter Like us on Facebook