Tony Abbott has delivered a blunt message to the man who replaced him as prime minister, warning Malcolm Turnbull not to break faith with the Australian people and allow a free vote on same-sex marriage in parliament.
Tensions within the government over same-sex marriage have erupted again after Fairfax Media revealed that moderate MPs are preparing a push for the Coalition to abandon its policy that a national plebiscite should be held before any vote in the Parliament.
A chorus of conservative MPs reacted angrily to the report on Saturday, saying any move to allow a free vote on the issue would be a "betrayal" of the Coalition's election commitments.
Same-sex marriage supporters in the Liberal Party argue for a vote to be held before the May budget and could raise the issue in the party room within the next fortnight.
But it is the intervention of Mr Abbott in the debate, a standard bearer for the conservatives in the Liberal Party, that is most significant and which underscores the political peril that will confront Mr Turnbull if he allowed his MPs a free vote.
Mr Abbott spoke exclusively to Fairfax Media to warn his successor there should be no free vote - a move that would almost certainly ensure same-sex marriage becomes legal as Labor and the Greens would also vote for the law change - and that the proposed plebiscite should remain party policy.
"Malcolm Turnbull made a clear election commitment that the marriage law would only change by way of people's plebiscite, not free vote of the parliament," he said.
"I'm sure he'll honour that commitment. This isn't about same-sex marriage, it's about keeping faith with the people."
Former cabinet minister Eric Abetz also spoke out: "The Prime Minister has made it crystal clear that the government's position is for a plebiscite or nothing.
"This position enjoys overwhelming support and most colleagues see this as an unhelpful distraction."
Sydney Liberal MP Craig Kelly told Fairfax Media: "The plebiscite was a black-and-white election commitment.
"To abandon that would be a betrayal of what people voted for at the last election.
"People are more cynical about politicians than they have been at any time in history and we have to show that we respect the policies we took to the election."
Mr Kelly said the Coalition should debate whether it takes the policy of a free vote to the next election, noting that is probably two-and-a-half years away.
Until then he said the Government should reintroduce the plebiscite to Parliament and try to convince the Senate to support it.
Nationals MP George Christensen, who along with Mr Kelly and Senator Abetz opposes same-sex marriage, said the plebiscite was a "key plank" of the Liberal-Nation Coalition agreement and should be maintained.
"There will be push back on any move to drop the plebiscite," Mr Christensen said.
"It would be a breach of the Coalition agreement.
"I don't think a plebiscite is a dead option in this term of Parliament - we should tweak it and try to get it through."
One conservative MP, who asked not to be named, said: "These ideologues [pushing for a free vote] are very damaging for the Government.
"I don't know how they think this helps us at a time we're under pressure on our right flank.
"One Nation will be rubbing their hands together.
"If this happened it would be a breach of faith that would result in a backlash against the PM and the government."
The MP noted that the most recent push for a free vote in 2015 was defeated in a joint party room meeting by 70 votes to 30 and questioned why moderate MPs think they have the numbers this time.
But Fairfax Media understands a pragmatic view has developed within cabinet - including among some ministers opposed to same-sex marriage - that a free vote should be held in this term of Parliament.
Liberal MP Warren Entsch, one of the Coalition's leading advocates of same-sex marriage, said: "At the end of the day we have to get this issue dealt with once and for all.
"My position hasn't changed one iota and it's not going to go away.
"I will work with people of like mind and see where we end up."
Mr Entsch said he would negotiate privately with his colleagues rather than through the media, but he believes the plebiscite policy is dead.
"The plebiscite was imposed on us by others but I gave it my best shot to get it over the line," he said.
"I have done everything I can to support the plebiscite - more than some who say they are in favour of it - but it's not going to happen."
Opposition Leader Bill Shorten said he would work with politicians from any party to make same-sex marriage a reality in Australia.