Acting opposition leader Tanya Plibersek wants Labor to force her colleagues to vote in support of legalising same-sex marriage.
Ms Plibersek will push the ALP's national conference in July to impose a binding vote on its federal MPs.
She says the existing conscience vote policy should be set aside, arguing it is not an issue of life and death.
"It's important for the Labor Party to say we don't agree with legal discrimination," Ms Plibersek told ABC Radio on Monday.
Labor's national conference four years ago voted to allow MPs a conscience vote on the issue despite the party's platform being supportive of gay marriage.
Labor frontbencher Bernie Ripoll is prepared to vote for same-sex marriage having opposed it previously, but wants a conscience vote across the entire parliament.
"Australia is ready," he told Sky News.
Prominent Labor figure Graham Richardson accused Ms Plibersek of wanting to impose a double standard on the party because she and other opposition MPs had been calling on the coalition to allow a conscience vote.
"I thought she was a lot smarter than that," he told Sky News.
Australian Marriage Equality spokesman Rodney Croome said the move could help break a parliamentary deadlock.
The normal practice of a Labor binding vote and a coalition free vote would allow Australia to finally achieve marriage equality, he said.
The Australian Christian Lobby wants the ALP to stand by Opposition Leader Bill Shorten's backing for a free vote, which he made at its conference last year.
"Mr Shorten made it very clear that Labor believed its parliamentarians should not be forced to redefine marriage," ACL managing director Lyle Shelton said in a statement.
Forcing Labor MPs to vote as a bloc would alienate a number of them from their socially conservative electorates, especially in outer-metropolitan electorates, he said.
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