NZ First leader Winston Peters has called for a referendum on gay marriage, but declined to say how he would vote on one.

Peters this afternoon said the eight New Zealand First MPs had agreed not to support the bill for "marriage equality" being promoted by Labour MP Louisa Wall.

"We will not be voting for this bill, we will argue for a referendum and we believe there should be enough members of parliament who have got confidence in the public of this country to trust the public to decide this issue after reasonable debate," Peters said.

However, he indicated he would make no contribution to any debate over gay marriage, saying his views on the matter were "irrelevant".

The public should be left to decide on the issue "rather than have people try to twist the public debate with their personal view," Peters said.

"Look at the record of parliamentarians on important social issues - they're all over the place," he said.

"These serious issues of this type should be decided by the public of this country and not a few temporarily empowered politicians."

Asked if the party's position meant all its MPs would abstain on the vote, Peters said: "I've just said that's what our position is and we're united on that."

Asked to confirm that the party would abstain, rather than vote against it, he said: "Well, we're not voting for it, is what I said. We believe it should be by way of referendum."

NZ First MP Richard Prosser has already indicated he would vote against the bill.

''I'll be voting against. I've said so in print. It's about preserving the institution of marriage...I've got nothing against gays. To me, marriage is an important institution on its own," Prosser said last week.

Peters voted against the Civil Union Bill in 2007.

- © Fairfax NZ News