Prime Minister Julia Gillard remains opposed to gay unions, putting her at odds with right-wing Labor powerbroker Mark Arbib.

Senator Arbib is the first frontbencher to say he believes his party should support gay marriage.

He says gay people should have the legal right to get married, and MPs should be given a conscience vote on the controversial matter.

"If I was the parent of a gay son or daughter I don't know how I could tell them they didn't have the same rights as I did," Mr Arbib told The Weekend Australian.

"I understand the Labor Party platform does not reflect that view at the moment but I hope one day that view changes."