Otago University law professor Andrew Geddis says former Green MP Darleen Tana is "grasping at straws" when they argue they are not disrupting Parliament's proportionality by staying on as an independent.
Tana (who uses the pronoun they/them) resigned from the party ahead of a caucus decision on whether to eject them, over the report which found Tana likely knew about allegations of migrant worker exploitation at their husband's business but did not tell the party.
Tana responded yesterday to the Green Party co-leaders' request they resign, saying they have no intention to do so.
Tana replied saying they were fairly elected as a list MP at the last general election, and they have done nothing which would require the Speaker to expel them from the House.
They argued their proxy vote is still being cast in alignment with the Greens, and the party would only lose one primary question every 47 days of Parliament sitting.
Tana also disputed the costs to the Greens' budget by no longer having 15 MPs.
In their response, Tana also referenced a Supreme Court case from 2005 (Huata v Prebble), saying "it is at the very least contestable that cessation in membership is in and of itself sufficient to meet the requirement as the distorting condition".
Greens co-leader Chlöe Swarbrick told RNZ's Morning Report programme today the situation was unprecedented.
"Something that has never occurred before for us in the Green Party, where we have come to a position saying that someone is not fit to be a Member of Parliament and they have also resigned from our caucus."
"We know that this is a serious decision."
The party will vote next weekend on whether to use the waka jumping legislation to have Tana kicked out of Parliament.
Green Party rules require 75 percent of the 200 delegates to support the use of the legislation.
"We're progressing as a party to make a decision on what happens," Swarbrick said.
She acknowledged the party's "vexed history" with the legislation but said their concerns stemmed from worries about a concentration of power with party leadership that would use it when someone stood on principle.
That was not the case here, she said.
Tana hanging interpretation on one quote
Prof Geddis, from Otago University's Faculty of Law, said Tana was hanging their interpretation on one quote from one judge.
"When you look at the facts of how the Supreme Court dealt with that previous case, they held that an MP who would relinquish their membership of the parliamentary party, had triggered the party hopping law, and that's basically what Darlene Tana has done here."
Geddis said Tana resigned from the Greens, causing the party to have one fewer MP, therefore, he said "on the Supreme Court's reading of the law, the proportionality of Parliament has been distorted".
"If an MP leaves their party, then that is grounds for the party to use the party hopping law to have them kicked out of Parliament."
Tana may not have realised that was what they were doing when they resigned from the Greens, but that was the effect of it, he said.
Geddis acknowledged different judgments in the Supreme Court ruling meant slightly different language or a slight differentiation in the way things were expressed.
"Darleen Tana appears to have latched on to one judge's expression of it to say, there's some doubt.
"I honestly don't really think there is. I think the grounds have been met as a matter of law."
Party delegates will vote next month on whether to apply the party-hopping legislation, which the Greens have historically been opposed to.
Geddis said if the Green membership did vote to invoke the party-hopping law, Tana could go to court and ask for an injunction to stop the law going through.
He said one issue with that is that it would be extraordinarily expensive and Tana would have to fund that.
Secondly, Geddis pointed out this decision - whether or not the party-hopping law has been triggered - was a matter of parliamentary privilege, which the courts were not allowed to look into, and therefore was "for Parliament to decide through the Speaker."
Tana could argue to the Speaker that based on their reading of the Supreme Court judgment from 2005, they have not breached the law, but he said he would be surprised if the Speaker were to take that reading of the case, he said.
"That's not to say he couldn't, but it would be extraordinarily surprising."
