NEXT STEPS IN SAME-SEX MARRIAGE DEBATE:
* Laws to allow a compulsory plebiscite go back to parliament this week for a vote. The key to its success will be the Nick Xenophon Team changing its position and backing the government. NXT opposes a plebiscite, but if the alternative is a voluntary postal vote it may put pressure on the party to back the compulsory vote.
* If the plebiscite bill fails again, the government will start work on a voluntary postal vote.
* If the bill succeeds and the plebiscite is passed by a majority of Australians, a private member's bill to change the Marriage Act will be brought to parliament and all MPs will have a free vote on it. The numbers are expected to be there for the law change to go through.
* If the bill succeeds and the plebiscite vote is a majority "no", the government won't support a marriage amendment bill to go forward, or another national vote. If Labor wins the next election it would legislate.
* The postal vote would likely be held before the end of 2017 and, if passed, the government would bring a private member's bill to parliament to change marriage laws. The details of the ballot have not been decided, but the government has advice it is within the constitution.
* Gay marriage advocates have advice a postal ballot is unconstitutional and would seek to challenge it in the High Court once the details and legal framework are known. This could delay the postal ballot outcome and the marriage bill coming to parliament.
* Labor has discussed the private member's bill drafted by WA senator Dean Smith and is happy with its wording. Labor members are allowed a conscience vote on the bill and only a handful will oppose it in the lower house and Senate.