The Crown has withheld highly relevant and crucial information about stricken container ship the Rena from the Waitangi Tribunal, Motiti Island groups say.
In 2011, the ship crashed into the Astrolabe Reef, off Tauranga, spilling tonnes of oil and debris into the sea and creating one of New Zealand's worst maritime and environmental disasters.
The Rena is owned by Greek shipping company Costamare through one of its subsidiaries, Daina Shipping Company.
In September, Radio New Zealand revealed that the New Zealand Government had sought independent advice after the Rena's owners applied for resource consent to leave most of the ship where it is.
The advice was in reports by London Offshore Consultants, which said that the owners grossly exaggerated the time and money it would take to remove it. They also rebutted claims that full removal of the wreck could cause more environmental damage.
The Crown is seeking that only some of the wreck be removed, partly because of the cost of full removal and the risk to people who have to do the job.
The Motiti Rohemoana Trust and Ngai Te Hapu have a case before the Waitangi Tribunal and are arguing for Rena to be fully removed.
The groups have told the Tribunal that the Crown could have had the independent reports before the end of their hearing, and the Crown appears to have failed to take into account its own expert advice.
Lawyers for the groups said the reports show that there are fundamental problems with the Rena owners' conclusions, and not releasing them has shown an apparent disdain for the role of the Tribunal.
The Crown rejected the allegations and said it would respond to them later this week.
It is not yet known when the Tribunal's full report into the Rena would be released.