The Turnbull government will put its doomed same-sex marriage plebiscite back before parliament for debate.
Cabinet minister Mathias Cormann has given notice he will move that the bill be restored onto the Senate's agenda on Wednesday.
The bill is almost certain to fail for a second time in the upper house after which the government will move to a $122 million postal vote, which does not require legislation.
Liberal and Nationals MPs on Tuesday endorsed a plan to have the Australian Bureau of Statistics - which is still reeling from last year's bungled census - conduct the postal ballot.
Handing the job to the ABS and using ministerial powers would get around the need for legislation passing parliament and potentially head off a court challenge by marriage equality advocates.
If the plebiscite bill is unexpectedly passed, a $170 million compulsory vote would be held on November 25.
A postal vote would see ballot papers in mailboxes from September 12 and a result declared on November 15. But there would be no publicly funded "yes" and "no" campaigns.
Prime Minister Malcolm Turnbull said if there was a majority "yes" vote the government would bring to parliament in the final sitting fortnight of the year a private bill, on which Liberal members could cast a free vote.
Attorney-General George Brandis expects same sex marriage to be legal by Christmas.
"Politicians have no special insight into the workings of the human heart and this is an issue so intimate, so personal, that it is almost uniquely the sort of issue that we want every Australian to have their say," Senator Brandis told ABC TV.