Wollongong MP Noreen Hay has led a rebellion against Labor federal counterpart Stephen Jones, winning a key motion in his seat of Throsby which undermines his public stance on same-sex marriage.
The humiliating defeat reflects widespread anger among ALP members in Mr Jones' electorate, who feel they were not consulted about his position on the issue.
Mr Jones plans to move a private member's bill in Federal Parliament to legalise same-sex marriages, putting him at odds with senior parliamentarians including Prime Minister Julia Gillard.
On Thursday, at a meeting of ALP branch representatives, Ms Hay, representing the Dapto branch, moved a motion emphasising that marriage should be between a man and a woman.
The motion was passed, to the chagrin of Mr Jones, who was also present. It will now be sent to the federal Labor Caucus, undermining Mr Jones' credibility on the issue in Canberra.
A gag order prohibiting discussion of the motion in the media was also passed on the night. One senior ALP figure present, speaking on condition of anonymity, told the Mercury Mr Jones was angry the motion succeeded.
Ms Hay would not confirm or deny whether she moved the motion, but did say: "I think it stands to reason that MPs will have different views" on same-sex marriage.
She agreed same-sex couples should be afforded the same legal rights as heterosexuals, but that marriage should remain between a man and a woman.
The issue also reflects ALP factional divides in the Throsby seat. Mr Jones is a senior member of federal Labor's Left faction while Ms Hay is the parliamentary leader of the NSW Labor Right faction.
Mr Jones' stance on same-sex marriage has exacerbated tensions in Throsby which have been brewing since he was "parachuted" into the safe seat after the departure of former member Jennie George in August 2010.
"Everyone ... is entitled to have an opinion, but he also has a responsibility to a community to gauge their community feeling," one ALP member at the meeting said.
ALP Shellharbour branch member Narelle Clay defended Mr Jones' position: "Stephen Jones' stand is a brave one and there are many examples where leadership is necessary, even if it is not the popular view," she said.
Mr Jones would not comment, because it was an internal ALP matter.
Email a friend