Labour MP Willie Jackson has warned Māori will "go to war" if a proposed referendum on Te Tiriti o Waitangi / The Treaty of Waitangi goes ahead under the new coalition Government.
It comes after ACT campaigned for a nationwide referendum on defining the three principles of Te Tiriti (The Treaty).
ACT leader David Seymour has said a referendum on Te Tiriti is a "bottom line" for his party's policies.
That's despite incoming Prime Minister Christopher Luxon ruling it out several times.
Luxon said it would be "divisive and not helpful" when he appeared on The Hui last month.
He reaffirmed that stance on AM on Monday.
"What I'm saying to you is that it's not National Party policy. We think it would be divisive and unhelpful."
Willie Jackson said on Tuesday if the ACT Party gets its wish granted for a referendum on Te Tiriti, he doesn't want violence or disruption.
"I'm not advocating for that at all," he told Newshub.
"But I do understand our people's frustration and anger if this was to go ahead."
Jackson said if a referendum on Te Tiriti gets pushed through, he'll stay on as an MP.
"If there's a referendum I'll stay around for as long as it takes to fight that, and to stop that.
"This is such an affront if that referendum comes forward," Jackson said, referencing Graham Latimer and Tā Tipene O'Regan, two Māori leaders who brought Māori grievances to the fore.
"I'm just giving a warning. I work amongst our people - I'm amongst people who will go to war for this, war against Seymour and his mates," Jackson said.
"I'm saying to you what Māori have been saying to me."
Labour MP Kelvin Davis, who stepped down as the party's deputy leader on Tuesday, said Seymour has been "speaking to his bubble".
"What gives them the right to unilaterally tutū with the Treaty when there are two partners to the signing - and yet one group is making a unilateral decision. I just don't think that's right," he told Newshub.
Davis said he had heard "a lot of concern" from Māoridom about ACT's referendum proposal.
"We've been looking at what has been said on the campaign around referendums, about fiddling with the principles of Te Tiriti o Waitangi, and that is a real concern."
Seymour needs to go to "his people", he said.
"He says he's from Ngāpuhi, he says he's from Ngāti Rēhia, but he's never ever gone to Ngāpuhi or Ngāti Rēhia and put his case."
"If he wants to get that referendum over the line, with the least possible disruption, he needs to get the validation from Māori in the first instance."
In response to Jackson's comments, Seymour told Newshub ACT wants "rational debate" on the topic.
"When people threaten war as the alternative to that, they are not being a good actor investing in the future of our country."
Seymour then doubled down on his party's policy.
"It's all the more reason why we should have a debate on The Treaty [of Waitangi]."
It comes amid coalition negotiations between National, ACT and New Zealand First, after the election's final vote count was released on Friday.