Prime Minister Malcolm Turnbull has declared a "no" vote in the same-sex marriage postal survey would see the Coalition rule it out of parliamentary consideration for both this term and the next, were he to win the 2019 election.
The statement raises the pressure on the "yes" forces to secure a positive outcome in the postal survey and increases the chances that the next election could see same-sex marriage emerge as a clear party-political contrast for the first time.
It may also increase the danger of a breakdown of Coalition discipline by pro-change Liberals if they decided to cross the floor to force the change, following a narrow "no" vote, especially if accompanied by a low turn-out.
Opposition Leader Bill Shorten has pledged to introduce a parliamentary bill to establish marriage equality if Labor wins, even after a negative postal survey result.
Voters would be offered a choice of a party proposing to make it law, and another committed to denying it.
In his most definitive comments on the subject since the controversial survey commenced last week, Mr Turnbull said Australians therefore faced a simple choice between approving the change to the Marriage Act, or rejecting it outright.
Immigration Minister Peter Dutton, who championed the postal survey after the plebiscite option was blocked in the Senate, said the government would need to put the issue behind it in the event of a "no" vote by the people.
"If the 'no' vote is successful, then I've been very clear as well, not only about my position but what I think the government's position should be, and that is that this matter is at an end for the Liberal Party, that there will be no change to the existing law," he told Sky News.
Asked about Mr Dutton's observation, Mr Turnbull agreed without reservation.
"Absolutely, it's very straightforward, if there is a 'yes' vote, then we'll facilitate a private member's bill to legalise same-sex marriage, and it there's a 'no' vote, we won't, that's it, very straightforward," he said.
"If the people have spoken against it, we won't be proposing it at the next election I can assure you."
With the two camps now campaigning strongly, Tony Abbott again weighed in on Tuesday, using a Sydney radio interview to complain the nation was being "frog-marched" into changing the definition of marriage while calling on the "yes" proponents - including Mr Turnbull - to detail before the survey period expires, precisely what religious protections would apply in the new law.
However, Mr Dutton, an influential conservative in the government, added to similar comments by Treasurer Scott Morrison on Monday, arguing it "wasn't possible" to spell out the religious protections before the vote.
Mr Dutton said the process had moved "fairly rapidly" once the postal survey was commissioned.
The cabinet's decision was to sort out the details in the aftermath of a "yes" vote through a private member's bill, Mr Dutton said.
"There will be a series of votes on aspects of that bill, there will be protections that some members will strongly support and others will strongly oppose," he said.
Mr Abbott argued there were many loving and stable relationships that were worthy of respect, including those between friends and between parent and child, but that didn't mean they could all attract the title of marriage.