Hunter MP Joel Fitzgibbon is accusing the Prime Minister of acting undemocratically in regards to the push to legalise same sex marriage in Australia.

Mr Fitzgibbon is now in favour of the change after previously speaking out against it, because he said his electorate was not ready.

A US Supreme Court ruling giving gay couples the right to wed has sparked celebration around the world and follows similar moves by other western countries.

Mr Fitzgibbon says Tony Abbott has some thinking to do.

"The Prime Minister now has a real problem," he said.

"The rest of the world is moving and it's clear the majority of people both in the House of Representatives and probably the Senate now support the change here in Australia.

"He's holding it back by holding them to a party vote and I think that's undemocratic, frankly.

Mr Fitzgibbon said the US Supreme Court ruling vindicates his decision to change his stance on the issue.

The ruling follows decisions in several western countries including Ireland, New Zealand, Britain, France and Spain to allow gay marriage.

He said Australia is practically standing alone in resisting the push for same sex marriage.

"I've considered the change inevitable for some time now.

"This issue in the US will give it more momentum but I think people just need to progress slowly and wisely and ensure that we take as many from the community with us as we can."