THE AUSTRALIAN GOVERNMENT has announced it will host a postal vote on marriage equality, if a bid to win support for a nationwide plebiscite fails in the Senate for the second time.

During the election campaign, the government of prime minister Malcolm Turnbull promised a "plebiscite", and intends to promptly return the folder in front of the Senate.

Australians are facing the possibility of a postal vote on same-sex marriage and if you want a say in the outcome it is crucial you're both enrolled to vote and have updated your details.

The proposed postal vote would cost more than 122 million Australian dollars (96 million dollars), Turnbull said.

"The Coalition supports the traditional definition of marriage between a man and a woman, but we won't seek to bind people beyond this term of Parliament and in the next will be the people's decision", Abbott said at the time.

Ballot papers are expected to be returned in early November, with parliament's last sitting before Christmas to decide on the issue.

If the plebiscite is passed, Cormann said the vote would be held on November 25.

Most Liberal MPs have called for the issue to be resolved swiftly to try to end a debate that has exposed the party's bitter internal divisions.

In an interesting move, it will also apparently be run by the Australian Bureau of Statistics (ABS), for reasons that will shortly become apparent.

"The Bill not only circumvents the government pledge for a plebiscite on the issue, it is manifestly deficient in its attempt to protect civil and religious freedoms for all Australians", he said.

Same-sex marriage is legal in a number of countries across the world, including Belgium, Canada, France, New Zealand, the United Kingdom, and others.

Basically, by framing the postal plebiscite as more of a statistical fact-finding mission than an actual plebiscite, the government reckons it can get it on the road without passing legislation.

The Equality Campaign dialled back its threat to launch legal action the day after a postal vote was floated, saying instead there was a "strong, strong prospect" of a challenge.

"Strong leaders carry out their promises, weak leaders break them", Mr Turnbull told reporters in Canberra on Tuesday.

Despite strong support for gay marriage, the country is seen by some as lagging behind nations that allow homosexual couples the right to Wednesday.

He said that if there was a majority "yes" the government would bring to parliament's lower house a private bill, on which Liberals could cast a free vote.

It looks likely Australia will vote in a national postal ballot on marriage equality in November.

"The postal vote. will give everybody their say".

Coalition backbencher Warren Entsch is reserving his right to cross the floor of parliament to vote against the government if the plebiscite fails.

Campaigners for same-sex marriage are confident the law will be changed if Coalition MPs are given a conscience vote on a bill.