New Zealand First leader Winston Peters has hit out at coalition partner Labour over its handling of the abortion legislation.

Photo: RNZ / Ana Tovey

After months of negotiations between the two parties, Mr Peters surprised both the Justice Minister Andrew Little and his own MP who'd carried out the negotiations with talk of a referendum earlier this week.

Mr Little said it was the first he'd heard of any referendum, and ruled out any deal in return for support from New Zealand First MPs.

Mr Peters has now told Sky News Australia his was the only party that's acted in good faith over the abortion legislation.

When asked why Labour had acted in bad faith he said: "It wasn't part of our coalition agreement so why is it there?"

"The fact that we were prepared to accept that they could put it there is a matter of good faith on our part," Mr Peters said.

If "anyone was blindsided", he said, it was New Zealand First, but they didn't "get upset and have a hissy fit".

"You should pay attention to other people's policies, I know what their policy is, they campaigned on it - we didn't.

"Did it come up in our coalition talks? No, it didn't."

New Zealand First wanting a referendum should have come as no surprise to Mr Little, said Mr Peters.

The Prime Minister would not be drawn on Mr Peters' criticisms of Labour, and her Justice Minister.

She said the process had been unusual as was a "different" piece of legislation, as it was "not a government bill".

There had been as much consultation across the board as possible, she said, because it was a bill individual MPs would vote on according to conscience.

"Parties don't tend to block vote on conscience votes so members of Labour will vote both for, and some will vote against, and so it has made it a different process than the usual legislation that we put before Parliament."

The Abortion Legislation Bill may be treated as a conscience matter, but it is still a government bill; it went through Cabinet, it's in the name of Andrew Little as the Justice Minister and is named as such on Parliament's website.

Ms Ardern was asked about Mr Peters' reference to it not being in the Labour New Zealand First coalition deal.

"It isn't a government bill, it shouldn't be characterised as a government bill, therefore you wouldn't expect it to be in an agreement."

She was also asked whether Mr Peters' comments about acting in good faith were helpful to the relationship.

"Ultimately parties will have their own perspective on this and members will have their own perspective on this conscience vote, and I expect that individuals will speak differently, even within their own parties... I take no grievance from taking different positions."

Ms Ardern did not however back away from the need to update New Zealand's law.

"I know this is a heated debate, I know this is one people feel strongly about, but we have not modernised our legislation since 1970 and what we're suggesting here is taking this out of the Crimes Act, and I think a large number of people would support that."

In a statement Mr Little had earlier said he was focused on the first reading of the Abortion Legislation Bill, which is this afternoon, and had no further comment.