Prime Minister Jacinda Ardern is under pressure to order an investigation into allegations swirling around donations to New Zealand First, as the saga risks hurting her coalition Government.
Allegations of electoral donation wrongdoing levelled against the coalition partner also appears to have put a dampener on the National Party's chances of working with NZ First after next year's election.
NZ First leader Winston Peters is remaining defiant after reports that the NZ First Foundation – a secretive body which collects party donations – appeared to have hidden political donations worth almost half a million dollars.
National Party leader Simon Bridges says if the allegations are true, they would be the "most significant allegations of this kind we have seen in New Zealand's history".
Bridges has always said his party would make decisions about ruling out any potential future coalition partners earlier next year.
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"It doesn't make a New Zealand First/National coalition more likely, that is for sure," he said of the saga.
Bridges is calling on the Prime Minister to launch an investigation into the questions raised over the allegations of electoral donation wrongdoing.
But Peters has been adamant the party has acted well within the rules outlined in the Electoral Act and says he plans to meet with officials from the Electoral Commission soon.
This is despite electoral law specialists, including University of Otago law professor Andrew Geddis and public law expert Graeme Edgeler, both questioning the legality of the foundation.
Peters has rejected claims of any wrongdoing, telling Newstalk ZB his opponents were trying to make a "mountain out of a molehill".
"We have had these accounts all properly audited by an official auditor that all political parties are required to have."
Peters insisted NZ First had always operated within the electoral laws and had always declared donations to the Electoral Commission.
He said he planned to discuss the matter further with the commission soon.
Peters told ZB that the issue showed there were political forces in this country that were "seriously worried about the growing strength and support base of New Zealand First".
But many questions still remain about the mysterious NZ First Foundation. Peters said several times that any questions about the foundation should be directed to the party.
"I'm not in charge of it," Peters said of the foundation.
This is despite former NZ First party president Lester Gray – who stepped down in September – telling the Herald the foundation was "nothing to do with my role as the president or the NZ First board".
Bridges was highly critical of both Peters and Ardern over the saga.
He said the Prime Minister needed to show leadership on this issue, and make sure it was thoroughly and independently investigated because it goes to the heart of New Zealand's democracy.
The Electoral Commission is looking into the allegations, but Bridges said that body was a "toothless tiger".
"It ultimately does not have anything like the powers to deal with this."
Bridges said it was up to the Prime Minister to choose who investigates the accusations and said if Ardern chose to, she could refer the matter to the police.
He also put distance between National and New Zealand First when it comes to any potential future coalition deals.
The situation "doesn't make it more likely that we will work with NZ First".