Shorten mum on Labor's plebiscite stance

Opposition Leader Bill Shorten won't publicly confirm whether he'll tell the Labor caucus to block the same-sex marriage plebiscite.

"Now the legislation has been tabled, we'll have a discussion at our next caucus meeting," he told reporters in Washington.

It's understood Mr Shorten will advise the October 11 gathering to reject the legislation for a public vote on the matter.

He maintains the plebiscite is not the best option.

"I have not yet heard an argument which is satisfactory for treating gay people differently, through a different policy making process than the rest of Australians."

He accused Prime Minister Malcolm Turnbull of being "weak" in not allowing parliament to decide.

"And if he needs us to be strong for him we will."