Labor Party members will push for a binding vote on same-sex marriage at their national conference.
The party's current position is to allow a conscience vote out of respect for the religious views of members.
But Labor frontbencher Penny Wong says it's a matter of discrimination, and party policy should reflect this.
"There are many people who are well on the record as saying we should have a binding vote when it comes to matters of discrimination - I'm one of them," Senator Wong told ABC radio on Monday.
Labor deputy leader Tanya Plibersek has also previously spoken in favour of a binding vote.
But there is no clear position within the Left faction of which Senator Wong and Ms Plibersek are members.
Senator Wong said the focus should meanwhile be on encouraging Prime Minister Tony Abbott to allow his MPs a free vote when a cross-party bill came to parliament.
Liberal MP Warren Entsch proposes to bring an amendment to the Marriage Act, sponsored by Labor MP Terri Butler, to parliament when it resumes after the six-week winter break.
But it remains coalition policy to support the status quo and any frontbenchers who wish to change the law would have to quit their posts to cross the floor.
At the weekend, Nationals deputy leader Barnaby Joyce said Asian trading partners could view Australia as "decadent" if gay marriage was allowed.
Senator Wong described that as an "inventive new excuse".
"Let's not beat around the bush - we should do it because Australians decide, as they have within the community, that couples should be treated equally regardless of the gender of their partners," she said.
Christine Forster, Mr Abbott's lesbian sister, says Australians are getting increasingly impatient waiting for politicians to make a decision the community has already reached.
She wrote in The Australian on Monday that a decision would free the government up to focus on economic and security priorities.
Meanwhile, Labor has preselected a gay army officer, Pat O'Neill, as its candidate for the federal seat of Brisbane.
