Australians would vote on whether to legalise same-sex marriage in a compulsory plebiscite on February 11, 2017, under a plan taken to cabinet on Monday evening.
The controversial topic will pose a major test of the Turnbull government's resolve and unity, and will also force Labor to finally reveal its hand and commit to either blocking or supporting the plebiscite.
Cabinet was set to debate and finalise the proposed plebiscite details before the Liberal and then Coalition partyrooms meet on Tuesday morning.
Government sources told Fairfax Media the question being considered by cabinet to put to voters is: "Do you support a change in the law to allow same-sex couples to marry?"
It is understood that the inclusion of the word "change" in the question is seen as crucial to helping secure the support of conservatives for the proposed wording.
Fairfax Media has also been told that cabinet heard arguments for and against public funding for the "yes" and "no" campaigns and that a figure of $7.5 million for each side was pencilled in, though this figure has not yet been agreed to by the party room.
Cabinet ministers including Scott Morrison, Peter Dutton, Mathias Cormann, Barnaby Joyce and Matthew Canavan were said to be among those arguing for public funding, whereas moderates led by Attorney-General George Brandis have argued internally that both sides should pay their own way.
The cabinet submission being considered by Prime Minister Malcolm Turnbull and his ministers would allow pre-poll and postal voting to begin up to three weeks earlier than the February 11 date.
Crucially, commercial media enterprises, such as television networks, would be forced to carry advertisements from both the "no" and "yes" camps and could not pick sides in the debate. This measure is the same as one put in place during the Republican referendum in 1999.
A spokesman for Senator Brandis said they did not comment on cabinet deliberations.
Mr Turnbull, accused of promising taxpayer money to church leaders earlier this year, on Monday hinted that public funds would be forthcoming, telling Parliament: "Any funding provided in respect of the arguments 'yes' or 'no' in the plebiscite will be provided equally in accordance with our past practice."
Liberal MP Warren Entsch, a veteran gay rights advocate in the Coalition, warned that such a plebiscite would likely fail to pass the Senate. "There will be no plebiscite, it won't get up," he told Sky News. "We wouldn't be able to get it through."
The Turnbull government needs Labor's support, with the Greens and Nick Xenophon Team committed to opposing it, and Victorian senator Derryn Hinch confirming in his maiden speech on Monday that he would do the same.
Labor leader Bill Shorten dialled up Labor's opposition to the plebiscite on Monday, introducing his own same-sex marriage bill and warning of the possibility of youth suicides because of a hateful and homophobic "no" campaign.
"Every piece of expert advice tells us young Australians who are gay are more likely to contemplate suicide and more likely to take their own lives," he said.
"Let me be as blunt as possible: a 'no' campaign would be an emotional torment for gay teenagers, and if one child commits suicide over the plebiscite, then that is one too many."
Labor MPs told Fairfax Media it was now all but impossible for the opposition to lend its support to the plebiscite, no matter what the question or structure.
"It is hard to walk back from that now," said Labor backbencher Anne Aly. "We just can't. A plebiscite will hurt too many people," said opposition whip Graham Perrett.
Mr Shorten's warning about suicides attracted the cautious endorsement of gay rights campaigner Rodney Croome, but criticism from Liberals. Mr Turnbull said his counterpart "demeans the people he claims to represent", while gay Liberal MP Trent Zimmerman warned that raising the subject of suicide could become "a self-fulfilling prophecy".
Marriage equality advocates, in Canberra on Monday to lobby MPs, are united in their opposition to public funding for the "yes" and "no" campaigns, while opponents have demanded $5million-$10 million be given to each side.
In a last-minute attempt to sway votes, Australian Marriage Equality chairman Alex Greenwich, high-profile physician Kerryn Phelps and key Liberal figure Paul Ritchie will address the Nationals partyroom on Tuesday morning.
They will advocate a free vote and demonstrate support for same-sex marriage in regional and rural Australia, but also argue the case against public funding for the plebiscite campaigns. "We don't need to add to the [$160 million] cost," Mr Greenwich said.
Last time the Coalition partyroom seriously debated the issue of same-sex marriage, in August last year, the meeting lasted six hours and resulted in the proposed plebiscite, which then prime minister Tony Abbott promised after the next election.
Mr Turnbull inherited that commitment and, despite his personal preference for a free vote in Parliament, has been forthright in his determination to honour the pledge.
