The Government is being warned it can't just change its mind, when it comes to Treaty settlements.

The Maori Party is offering to mediate, in a last ditch effort to help National and iwi reach an agreement over the Kermadec Ocean Sanctuary.

MORE: Zero chance of Kermadec dispute escalating further with Maori Party - PM

The matter is now heading to the High Court, with iwi saying it would take away fishing rights granted to them in a 1992 settlement.

Co-leader Te Ururoa Flavell said he's happy with any solution that iwi agrees to, but the Government needs to make the effort to mend bridges.

"Our people won a Treaty settlement fair and square and if a piece of legislation comes over the top of that and takes away those rights, then of course that's where our issue lies," he said.

Mr Flavell said any agreement that can be reached is fine by them, as long as both Maori and the Government accept it.

"What we're trying to do is get it back to the table and start again, because the process at the beginning is acknowledged by most parties as a little bit sub-standard in terms of engagement with iwi."

But Environment Minister Nick Smith is digging in his heels, saying Maori were only given quota rights, not property rights, so can be overruled.

"It has always been true that under our quota management system, the Government retained the right to create areas of marine protection. That is also the same regime that operates in other countries."

Mr Smith said he's confident the law is on his side, as it's been tested before.

"There have been 20 different marine protected areas created since the fisheries settlement was done in 1993, and a number of those other marine protected areas that were created had a greater practical impact."