It's unlikely Australians will be asked this year to vote on whether to allow same-sex marriage, but the Turnbull government won't publicly confirm a February plebiscite.
The Australian Electoral Commission has strongly recommended the government not hold a national vote on the issue before the end of 2016.
But the prime minister's office and senior ministers insist the timing and question are still to be decided by cabinet.
Malcolm Turnbull and colleagues had repeatedly said they hoped to hold the vote this year.
News Corp reported on Sunday he is expected to announce the plebiscite timeline, aiming for February, at a coalition partyroom meeting on September 13.
And Australians would be asked the simple question: do you approve of a law to permit people of the same sex to marry?
But a spokeswoman for the prime minister said the government's promises around holding the national vote as soon as practicable had not changed.
Minister Kelly O'Dwyer said cabinet was yet to make any decision on the timing or question, so no assumptions should be made.
The AEC has previously estimated a national vote would cost taxpayers $160 million - not including funding for publicly arguing the cases for and against.
Opposition Leader Bill Shorten has criticised the expense of the exercise, especially since it won't even lock MPs in to vote the same way as the majority of Australians.
"Mr Turnbull is willing to waste taxpayers' money and provide a platform for hate campaigns, all because he doesn't have the guts to put a vote to parliament," he told AAP in a statement.
"Let's just get on with it."
Same-sex marriage advocates want the LGBTI community to be consulted over the timing of any plebiscite.
"We did not ask for a plebiscite, but if one is being imposed it's vital the question, process, and timing is fair and delivered in consultation with the LGBTI community and all political parties," NSW state MP and Australian Marriage Equality chair Alex Greenwich said.
GetUp said Mr Turnbull could instead hold a parliamentary free vote on marriage equality within weeks.
Greens Leader Richard Di Natale wasn't surprised to see the plebiscite potentially pushed back to next year.
"Delays are the entire point of the Liberals' plebiscite ploy. They don't want to end discrimination in the law, they want to push it off to the never-never," he said.
