A federal Labor backbencher opposed to gay marriage has called for a referendum on the issue.

John Murphy is a member of the New South Wales Right, and says Labor MPs who support gay marriage should join the Greens.

He says the majority of people in his inner-western Sydney seat of Reid are overwhelmingly opposed to same-sex marriage.

"The families that I talk to, they want a mother and a father," he said.

"They don't want two fathers and they don't want two mothers.

"I believe overwhelmingly the people of Australia will tell all those who are elected to represent them that allowing people to get married under the Marriage Act is a step too far."

Mr Murphy wants a referendum held on the issue or for MPs to get a conscience vote in parliament.

The majority of the ALP's state branches support same sex marriage and the issue is expected to be debated at the party's national conference in December.

New South Wales Labor Senator Doug Cameron is from the party's Left and says he respects Mr Murphy's opinion but does not agree with it.

"Without pre-empting the outcome, I think the odds are pretty high that the national conference will recognise that Labor party members who are gay, all Australians who are gay, should be treated equally," he said.

Federal Parliament has agreed to set aside time next month for MPs to speak for five minutes on the issue of gay marriage.

Last November, Parliament passed a Greens motion calling on MPs to consult their constituents about who should be entitled to marry.

The House of Representatives has since agreed that members should report back in mid-August on those consultations.

Recent polls have shown a slim majority of public support for changing the Marriage Act, but both Prime Minister Julia Gillard and Opposition Leader Tony Abbott have expressed opposition to any amendment.