The Australian Opposition Labor Party has given its strongest indication that it may block a public vote on same-sex marriage.

Labor leader Bill Shorten has called a plebiscite, as proposed by Prime Minister Malcolm Turnbull, as the “second-best option”.

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Speaking on Sunday in Melbourne, Shorten said: “We want to have marriage equality and we want to do it as quickly as possible.

“A vote in the parliament is the quickest, cheapest, least divisive mechanism.”

A plebiscite, or public vote, has been criticised as a stalling technique, and for costing taxpayers in Australia estimates of hundreds of millions of dollars.

In addition, the public vote would be non-binding, and would have to be followed by a parliamentary vote in order to make same-sex marriage law.

This is despite a majority of parliamentarians in Australia having indicated that they are pro-same-sex marriage.

But Prime Minister Malcolm Turnbull has hit back, suggesting that the plebiscite would be the quickest way to legalise same-sex marriage.

He told ABC TV: “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.”

The Australian Green Party has already indicated that it will oppose the plebiscite but has admitted being unable to block it without Labor’s input.

But Turnbull remains adamant that Labor will allow the vote to go ahead, and that arguing against the plebiscite in case the no-vote wins is “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,” he added.