Justice Minister Andrew Little says it would be "a bit cheap" to do a deal with the Greens in exchange for their support for the waka-jumping bill - but it is generally not uncommon for parties to do some horse-trading.

His comments come as a Green Party internal email - accidentally sent to Fairfax - revealed that the Greens were considering trying to get a National Day to commemorate Parihaka in exchange for support over the waka-jumping bill, a key part of the Labour-NZ First coalition deal.

The idea quickly ruffled the feathers of Little and New Zealand First leader Winston Peters, who said the policies should not be horse-traded.

NZ First MP Shane Jones added that the Greens could benefit from some expert advice from Helen Clark's number two, Heather Simpson, who is currently working in Jacinda Ardern's office.

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"The sooner that Heather Simpson goes to visit the Greens, the better," Jones said. "The waka-jumping bill is an important bill. It played a key feature in the development of the Government."

A waka-jumping bill is a new addition to the Government's 100-day plan and would ensure a party's proportional representation in Parliament, if an MP left a party.

The Greens have opposed waka-jumping in the past, but with National expected to oppose the bill, the Government would need support from the Greens to get the law over the line.

"Supporting the bill would be seen as changing and weakening a long-standing and public party position," said the internal email, from Greens' justice spokeswoman Golriz Ghahraman.

"Opposing the bill would cause political tensions, given the inclusion of the bill in the Labour-NZ First coalition agreement."

Little told the Herald that Ghahraman had not raised the idea of a National Parihaka Day in their discussions, nor had she suggested that the Greens might oppose the waka-jumping bill.

He said horse-trading over this issue would be poor form.

"Chris Finlayson, as [former] Treaty Negotiations Minister, had got to the point of a special agreement and settlement around Parihaka, and allowed the healing to start. It would be a bit cheap to tie that to a piece of legislation that is part of the coalition agreement."

But he said in general terms, horse-trading wasn't unusual.

"There will be times when parties will look for opportunities to seek an exchange. I just don't think this is one of them."

Ghahraman declined to comment.

Winston Peters poured scorn on horse-trading tactics.

"We're not going to do deals. This is a matter of principle.

"And the principles are, if waka-hopping destroys proportionality, it has to be dealt with. If Parihaka is a meritorious [idea], then it should be dealt with separately."

Prime Minister Jacinda Ardern said doing a deal with the Greens over waka-jumping had not come up "in direct conversation".

She said she has not given much thought to a National Parihaka Day.

"I certainly am pleased to see greater observance of those days of New Zealand's history. I think we should encourage that. Whether or not it becomes a day off is an entirely different issue."