Labor to block same-sex marriage vote

Prime Minister Malcolm Turnbull's plan for a same-sex marriage plebiscite looks to have run its race, with Opposition Leader Bill Shorten signalling Labor will block it.

Mr Shorten has told Fairfax Media he fears a popular vote will fail and set back the cause.

"I'm worried Malcolm Turnbull will just stuff it up," he is quoted as saying.

"He stuffed up the republic referendum, he stuffed up the NBN and he stuffed up senate reforms when he promised to fix it."

The Sydney Morning Herald says Mr Shorten's leadership group discussed the issue behind closed doors last week and while no final decision was made, they appear likely to vote the plebiscite down.

The paper says Labor fears Mr Turnbull will put no effort into the "yes" campaign allowing the well-organised and well-resourced "no" campaign to steal a march and ultimately carry the day.