Members of Port Nicholson Settlement Trust are taking a claim to the Waitangi Tribunal over what they say is the illegal sale of ancestral land at Wellington's Shelly Bay.
The trust purchased the land in 2009, using money acquired in a treaty settlement - but recent debate around the sale has divided its members, some of whom say they were not properly consulted about the sale.
A referendum held in February on whether to sell the land to a local developer, the Wellington Company, failed to reach the required 75 percent majority.
But last week the trust announced it would be entering into a proposed joint venture with the company, which would involve the sale of some Shelly Bay land, while the rest would be leased or retained by the trust.
The trust would stand to gain between $5 and $7 million from the partial land sale.
Because the amount of land being sold would not equate to half the trust's assets, it was not required to hold a referendum for the sale to go through.
A trust member, Kara Puketapu-Dentice, said Māori protocol had been overlooked in favour of commerce, and the sale of the land was "in breach of the Treaty of Waitangi and therefore illegal".
"Business has been placed above our values as Māori people, and our tikanga has been totally neglected through the sale of this land.
"Nothing in this proposal speaks to the values of our old people, and speaks to the values of our tupuna," Mr Puketapu-Dentice said.
But the trust's chair, Neville Baker, said there were elections coming up, and suggested the outrage expressed by dissenters had an ulterior motive - to remove him from his position.
Mr Baker said the trust's commercial wing, Taranaki Whanui, had a proven track record of making judicious decisions - and the Shelly Bay sale would be for the best in the long-term.
"Look at the performance of the trust and of the commercial board: prior to that, the trust was going broke. Because it was being badly managed, and was badly led by the chairman.
"That's been turned around."
But Mr Puketapu-Dentice said that was a disingenuous argument.
"How can it be in the long-term interests of the trust when it's the sale of land?
"Who is he to determine what is in the long-term interests of the trust when he had not actually consulted or engaged with the members?"
The trust will hold its annual general meeting in October.