Australia's same-sex marriage national vote cast into doubt

Australia's opposition party has given the strongest indication that it will block a national poll on the legalization of same-sex marriage.

Bill Shorten, leader of the Australian Labor Party (ALP), said he had a number of problems with Prime Minister Malcolm Turnbull's proposal to decide on the issue by a national plebiscite.

Without the support of the ALP, Turnbull would need to secure the votes of nine Senate cross-benchers to pass the legislation enabling the vote with the Greens having already announced they would not support the plebiscite.

Shorten cited the failures of the National Broadband Network (NBN) and Australia's failed republic referendum in 1999, in which Turnbull led the 'yes' campaign, as reasons not to trust the premier.

"He stuffed up the republic referendum, he stuffed up the NBN and he stuffed up Senate reforms when he promised to fix it," Shorten said on Sunday.

"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."

The plebiscite has drawn widespread criticism on account of the cost expected to top 120 million U.S. dollars and a potentially divisive public debate in the lead-up to the vote.

Despite Shorten strengthening his anti-plebiscite language, Turnbull said he remains confident the plebiscite would become reality.

"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," Turnbull told the ABC.

"Personally, I have no doubt the plebiscite will be carried and the same-sex marriage legislation will then sail through Parliament." Endit