Māori Party co-leader Rawiri Waititi is not surprised Labour wants to scrap the rule that brought in their second MP because it would "remove the only true and independent Māori voice from Parliament".
The rule is known as 'coat-tailing'. It allows political parties to bring in extra MPs without having to cross the 5 percent threshold if they win an electorate. The number of additional list MPs is based on the percentage of the party's vote.
The Māori Party was able to bring in an additional MP thanks to this rule. Waititi won the Waiariki electorate from Labour and he was able to bring in co-leader Debbie Ngarewa-Packer based on the party winning 1.2 percent of the vote.
Labour and the Greens don't think the rule is fair. They think it would make more sense to scrap the coat-tail rule and instead lower the threshold from 5 percent to 4 percent for parties to get into Parliament, which was recommended in 2012 by the Electoral Commission.
In a 2011 referendum, voters opted to keep the current MMP voting system which prompted an independent review of it. The recommendations included "abolishing the one electorate seat threshold for allocating list seats" - in other words, scrap the coat-tail rule.
Progressing the Electoral Commission's recommendations has been Labour Party policy since 2012 and Ardern recently signalled her intention to act on them after she was re-elected by a landslide. But Ardern intends to seek consensus.
"I believe the current Parliament is uniquely positioned to address these long term issues and find a consensus on them, and judging from recent public comment there appears to be an appetite across Parliament to take action on at least some of these issues."
Ardern says her view is that "if you win your seat you come in on that basis".
Waititi is not surprised Labour wants to get rid of the coat-tail rule because it allowed the Māori Party more representation in Parliament, and Labour currently holds all but one of the seven Māori electorates.
"Of course Jacinda Ardern supports getting rid of the coat-tailing rule in Parliament because this arrangement would remove the only true and independent Māori voice from Parliament," he told Newshub.
"Until we can completely reform the electoral law, the current law around coat-tailing is the only way Māori have an opportunity to extend their voice in Parliament."
He described the current electoral system as "inherently racist" and "intentionally blocks our right to equitable representation" because New Zealanders have to wait six years before they can switch from the general roll to the Māori roll.
"The Māori Party's mana motuhake policy sets out to decrease the party threshold to 2.5 percent and commit Māori to the Māori roll to gain an extra 12 or so seats. It's about levelling up the playing field so tangata whenua can participate at full capacity in the democratic process of this country."
Will Labour get consensus?
ACT has also benefited from the coat-tail clause. In 2008, it won 3.6 percent of the vote but got a total of five seats in Parliament because then-leader Rodney Hide won the electorate of Epsom.
New Zealand First won 4.07 percent of the vote in 2008 but because the party did not win a seat they did not get into Parliament.
National continues to do deals in Epsom with ACT. The National candidate doesn't campaign for the electorate vote and instead encourages its voters to vote for ACT in the hope it will piggy bank more MPs into the Parliament.
Although National did the deal in Epsom this election, ACT leader David Seymour didn't need it because ACT got 7.6 percent of the vote, crossing the 5 percent threshold on its own.
"Jacinda Ardern needs to explain why she is so determined that Māori Party voters shouldn't get their full representation and Debbie Ngarewa-Packer should not take her seat in Parliament," said Seymour.
"Election rules should be changed rarely, and only for good reason. Labour has no good reason to change the election rules other than its own political advantage."
National has been accused of maintaining the rule because it benefitted ACT.
Judith Collins was Justice Minister in 2012 when the MMP review was released and she did not act on the recommendations. Then-Labour leader David Shearer said National was pandering to its ally ACT and worrying about its own interests.
"The Government chucked it all out only because of very narrow political interests, its own interests of course, to keep Mr Banks in Epsom and try and bring a few ACT MPs behind him."
But Collins says there was no consensus at the time.
"When it was last reviewed there was no consensus in Parliament and I always took the view that we should have a consensus in Parliament on major constitutional issues," the National Party leader said this week.
Collins said she would be willing to see what the Government proposes. But she doesn't personally agree with bringing the threshold down for parties to enter Parliament.
"Our party has always taken the view that if you go to 4 percent then why not 3 percent, why not 2 percent, why not 1 percent? Five percent shouldn't be that hard for certain parties to be able to get to," she said.
"I think there can be chaos when you have proliferation of many smaller parties."
The Greens are on the same page as Labour.
"The Green Party have consistently called for the implementation of the full suite of our Electoral Commission's 2012 MMP Review recommendations, which the National Party ignored at the time," electoral reform spokesperson Golriz Ghahraman told Newshub.
"Now is the time to put this in front of Parliament - we believe the independent expert role of the commission and submitters should be honoured."
