Malcolm Turnbull is holding onto hope his same-sex marriage plebiscite will go ahead despite Labor giving the clearest indication yet it will block it.
Labor leader Bill Shorten says the plebiscite is a "second-best option" and his party appears to be leaning towards rejecting it.
"We want to have marriage equality and we want to do it as quickly as possible," he told reporters in Melbourne on Sunday.
"A vote in the parliament is the quickest, cheapest, least divisive mechanism."
But the prime minister indicated only holding a plebiscite would lead to a parliamentary vote.
"There is no question that the fastest way, the way to guarantee that there is a vote in the parliament on gay marriage in this parliament, is to support the plebiscite," Mr Turnbull told ABC TV.
Marriage equality advocate Rodney Croome, who opposes holding a plebiscite sure to be divisive and hateful, says if the prime minister really wants the change, he needs a back-up plan in case the Senate blocks it.
Labor is also worried about the plebiscite's success with the prime minister handling the national vote, saying he "stuffed up" the republic referendum, the NBN and senate reforms.
The opposition's leadership team has discussed whether to allow the plebiscite legislation to pass, but didn't reach a decision and may yet go to a caucus meeting.
The Greens have announced they will oppose the plebiscite and the government is unlikely to be able to convince enough crossbenchers of its merits to pass it without Labor's help.
Mr Turnbull still believed Labor would allow the plebiscite to happen.
Arguing that it shouldn't because the no vote might win was "the most anti-democratic argument".
"The Labor Party must want to delay same-sex marriage for a very long time, if they are briefing that."
The Australian Christian Lobby says it's disappointing that those advocating to allow same-sex marriage don't seem to trust people to have their say.
"This is an issue that has been prosecuted by fatiguing members of parliament over many years," director Lyle Shelton said.
"It is only right that the issue now goes to the people to decide what is a very big change with big consequences."
Coalition backbencher Warren Entsch, a long-time supporter of same-sex marriage, says the government would cop flak for backflipping on policy if it didn't go ahead with the plebiscite.
"I say this to the marriage equality people too: we won the election, we made a commitment to do this. Come on board and say, 'how can we help you'," he told Sky News.
"This is by far the most practical way and the most positive way of dealing with this matter and getting a positive outcome for it."
He didn't think either side of the argument should get public funding to make its case.
