New Zealand First's Winston Peters has labelled the Greens "unstable and untrustworthy" after the left-wing party supported National's attempt to repeal the waka-jumping legislation.
The Electoral (Integrity) Amendment Bill - commonly known as the waka-jumping Bill - was passed in 2018 as part of Labour and New Zealand First's coalition agreement. It allows party leaders to expel their members from Parliament if they break from the party.
While the Green Party has voiced opposition to such legislation in the past, it supported the Bill to keep "stability" in the Government, in which it is a confidence and supply partner.
But the Greens on Wednesday night supported a Member's Bill from former Speaker of the House David Carter to overturn the legislation. The Bill passed its first reading with support from National, the Greens, ACT and Jami-Lee Ross.
The Greens' support elicited a strong response from Peters, who said they had proven "themselves unstable and untrustworthy".
The Deputy Prime Minister said there was a "certain irony" in the Greens' support and dismissed any suggestion he negotiated for the waka-jumping Bill during coalition talks out of fear of one of his MPs jumping ship, as they have done so before.
"The Electoral (Integrity) Amendment Act was the result of the Labour-New Zealand First Coalition Agreement, but its genesis can be found in New Zealand First's view that if any party would fly apart during the electoral term it would be the Greens," he said.
"That is why the legislation was advanced, not out of any concern about my caucus but rather acute concern about the Green muster."
Peters said he didn't expect Green Party supporters would be "thrilled" their party had voted with National.
"By its actions the Green Party has demonstrated to voters that its word cannot be trusted. That is fatal," he said.
"When a party can't keep its word or commitments to its Government partners, freely given, voters are entitled to view that party as untrustworthy."
While the waka-jumping Bill promise doesn't appear in the Labour-Greens confidence and supply agreement, the Greens said they agreed to "act in good faith" to allow the coalition agreement to be complied with.
The Greens' Chlöe Swarbrick spoke on the Member's Bill on Wednesday night, saying the party would "honour our 20-year position on voting on this legislation tonight in much the same way that we honoured the coalition agreements and voting for the legislation that originally put it into place".
According to RNZ, co-leader James Shaw has said the Greens never made any commitment that should a repeal Bill emerge, that the party wouldn't support it.
Among the other speakers on Wednesday was National's Nick Smith, who called the waka-jumping legislation the "worst Bill of the 52nd Parliament".
"There is a very fundamental point of what makes a country a democracy and it is this: the people elect its members of Parliament and the people alone are entitled to fire them - the people alone are entitled to fire them."
New Zealand First's Tracey Martin said members who leave parties should seek the mandate of the people again, arguing that many are elected due to the party they are aligned with.
She called on the Greens to "keep one's word" and oppose the Bill.
"There is a time and a place to acknowledge commitments made and stick with them, and I'll be interested to see later tonight whether the Green Party has the integrity to vote their word, as opposed to deciding in the final days of a Parliament that they don't need a relationship any more, going forward, that they don't need to keep an agreement or a word given, and we will see what the Green Party does with regard to their integrity."
Parliament will be dissolved on August 12 ahead of the September 19 election. On the latest Newshub-Reid Research polling, New Zealand First would not return to Parliament unless it won a seat, while the Greens sit just above the threshold on 5.7 percent.