Treasurer Scott Morrison has urged same-sex marriage opponents to speak out, as he rejected claims the timing of the national vote has been set.
Attorney-General George Brandis has said the plebiscite to change the Marriage Act would be held later this year.
But he was contradicted by Prime Minister Malcolm Turnbull who said it would be held "as soon as possible" after the federal election.
Mr Morrison, who opposes same-sex marriage, said none of the details of the vote had been decided beyond the fact that a plebiscite would be held.
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"There's no change to the policy - the policy is to have a plebiscite," he told 2GB radio on Monday.
"The details of how it is constructed and the question and all of those sorts of things - that is still detail to be worked through and that will go through the normal cabinet process, including the ultimate timing of these things."
Asked whether he would take a backseat approach to the plebiscite, Mr Morrison said: "I don't plan to keep my opinion to myself on these issues and I don't think anyone should - that's the whole point of having a plebiscite."
Shadow attorney-general Mark Dreyfus said the plebiscite should be scrapped.
"They need to get their stories straight, but most of all Mr Turnbull should be dropping this wasteful and very divisive plebiscite," he told ABC radio.
"Let parliamentarians do the job we are meant to do, which is pass laws, to legislate."
A Labor government would have a bill to legalise same-sex marriage before parliament within 100 days of the election, he said.
Dumped cabinet minister Eric Abetz, who opposes same-sex marriage and has insisted he won't be bound by the plebiscite result, said the Brandis comments came as a surprise.
"These are matters that the party room still has to sort out in some detail," he told The Australian.
"If we were to have a plebiscite before the end of the year, and you were to reverse-engineer that, it would make interesting speculation about the timing of an election."
Greens MP Adam Bandt said the plebiscite proposal was "shambolic".
"It's not even clear that the government knows how to bring it into effect legally," he told ABC radio.
Cabinet minister Simon Birmingham said a plebiscite would be held in a "reasonable timeframe, as soon as is practical after the election".
But he refused to say whether it would take place before the end of the year.
"The government's intention is to go full term if we can, bearing in mind there are those important issues around the dysfunction of the Senate," he told ABC radio.
There is speculation a double-dissolution election could be called for July.
A July election would take pressure off the electoral commission as it plans for the $160 million plebiscite later in the year.
