Keep marriage a conscience issue: Bill Shorten

Labor is expected to retain a conscience vote on same-sex marriage, despite calls for MPs to be compelled to vote for it.

Some members of the party's Left faction want marriage equality to be firm policy, rather than a matter of conscience, and are working on a motion they want debated on the final day of the ALP national conference.

The party on Saturday reaffirmed support for same-sex marriage in its policy platform. But Labor leader Bill Shorten will tell the 397 delegates to the Melbourne conference on Sunday any move for a binding vote on MPs could backfire.

He will say it would undermine a bid to convince Prime Minister Tony Abbott to allow his frontbenchers a free vote on the issue when a cross-party bill is brought to parliament.

"I know we can achieve marriage equality by the power of our arguments," he will say.

Mr Shorten said in his opening speech to the conference on Friday that same-sex marriage would make Australia a more inclusive nation.

Deputy leader and Left faction member Tanya Plibersek has argued in favour of a binding vote.

But Left colleague Anthony Albanese, who supports gay marriage, says the party should respect those who oppose it on religious grounds.

The conference on Saturday voted in favour of gay, lesbian, transgender and intersex couples having the same access to IVF, adoption and domestic surrogacy arrangements as heterosexual couples.

Labor MP Terri Butler plans to co-sponsor a private member's bill with Liberal MP Warren Entsch to change the Marriage Act. But its success will depend on coalition MPs having a free vote.