The Federal Opposition has issued the strongest indication yet it could block a plebiscite being held on the question of same-sex marriage.
But Prime Minister Malcolm Turnbull said he still believes Labor will support legislation in Parliament to establish the nation-wide vote.
Labor and the Greens have voiced concerns about the cost of the plebiscite, as well as the prospect of a potentially divisive public debate on the issue.
In a statement, Opposition Leader Bill Shorten said he was worried the Prime Minister would "stuff it up", citing Mr Turnbull's handling of the republic referendum in 1999.
"He stuffed up the republic referendum, he stuffed up the NBN and he stuffed up Senate reforms when he promised to fix it," Mr Shorten said.
"Malcolm Turnbull doesn't even support a plebiscite. He's only doing it because he is too weak to stand up to the radicals in his own party.
"Why should everyone else have to pay for his weakness?"
Labor frontbencher Ed Husic said same-sex marriage could be made legal with a simple vote in Parliament instead.
"I think there are a number of us, and I certainly am of the view that we should get on with the vote, make the decision, do what the Parliament is supposed to and provide for marriage equality," Mr Husic said.
But Mr Turnbull said a plebiscite was still the quickest way to legalise same-sex marriage and that Labor was attempting to call the Coalition's bluff on the issue.
"There is no question that the fastest 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 Insiders.
"I think Labor will support it.
"Personally, I have no doubt the plebiscite will be carried and the same-sex marriage legislation will then sail through the Parliament.
Senior Liberal minister Christopher Pyne accused the Federal Opposition of playing politics with gay and lesbian couples in Australia.
"Labor is basically thumbing their nose at gay couples having the same status as different sex couples" Mr Pyne told Sky News.
"They are the villains in the piece."
He said if the plebiscite legislation was carried in Parliament, he could "guarantee" the vote would be held early next year.
The Prime Minister will need nine of the 11 crossbenchers in the Senate to pass legislation for the plebiscite, if the move is opposed by Labor and the Greens.
Greens leader Richard Di Natale on Friday confirmed his party would vote against the bill enabling the plebiscite, citing concerns from gay marriage advocates that the debate could see young people take their own lives.
Crossbench Senators Nick Xenophon and Derryn Hinch have also expressed reservations about the plebiscite.
Coalition backbencher George Christensen on Saturday said it would suit him if Labor and the Greens blocked a vote for a plebiscite on same-sex marriage.
He told reporters in Brisbane that while was in favour of the plebiscite, he did not want to see the Marriage Act changed.
"It's a policy that before any change to the Marriage Act, you have to have a plebiscite, so if Labor and the Greens don't want a plebiscite, that's fine, we'll just have no change to the Marriage Act in this Parliament," he said.
"That suits me, it will suit a lot of other conservatives as well."