Backlash over MP's stand against gay marriage! A federal Labor backbencher who wants his party's gay marriage supporters to join the Greens is facing a backlash from his grassroots support base.

John Murphy, a western Sydney MP for the seat of Reid, last week said he did not believe there was overwhelming public support for same-sex marriage and wants a referendum on the matter.

Mr Murphy said Labor members who support marriage equality should "join the Greens".

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The Lidcombe branch of the ALP has carried a motion in favour of marriage equality.

Branch president Gina Wilson said her members wanted Mr Murphy to acknowledge that he did not speak for the Lidcombe branch when he spoke against gay mariage.

Mr Murphy's call for a referendum was not representative of the views his electorate, she said.

Gay marriage supporters say there is no constitutional change required to amend the Marriage Act to allow same-sex couples to wed.

A new Roy Morgan poll has shown support for marriage equality is as high as 68 per cent.