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 Green Party's justice spokeswoman Golriz Ghahraman, in an internal email accidentally sent to Fairfax, floated the idea of trying to garner support for a National Parihaka Day - the subject of a Green private member's bill.
"The Government won't have the numbers to pass the [waka-jumping] legislation without us, and if we decided to oppose it then they would need to consider other options such as approaching the National Party, who opposed the 2005 bill," the email says.
"Opposing the bill would cause political tensions, given the inclusion of the bill in the Labour-NZ First coalition agreement.
"Our Confidence and Supply Agreement gives us the independence to choose to vote against it. Supporting the bill would be seen as changing and weakening a long-standing and public party position. It would risk criticism from our core supporters."
During the parallel coalition negotiations, Green's co-leader James Shaw put his faith in Jacinda Ardern to ensure that there was nothing in the Labour-NZF deal that the Greens would object to - though he conceded there might be policies that he might not be comfortable with.
New Zealand First leader Winston Peters poured scorn on horse-trading tactics.
"We don't horse trade. We don't trade principles ... 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. But we should not, surely, you would think in 2017, be trading these matters."
Peters said he was not aware of any discussions to do with the waka-jumping bill and Parihaka.
"Maybe they're having discussions with somebody else, but not with New Zealand First."
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."
Ghahraman declined to comment when contacted by the Herald this afternoon.
A spokesperson for the Green Party said the email was an "internal document that was sent in error".
"It's not surprising that Labour Party and Green Party MPs are having these kinds of constructive conversations and working together; in fact, that's what New Zealanders expect of government parties.
"It's commonplace for ministers and MPs to have these kind of conversations - that will continue," the spokesperson said.
