Waitangi Tribunal jurisdiction backdated to 1840

When the Waitangi Tribunal was set up in 1975 it could hear claims only about Crown actions taken from then on. Te Ara notes that at first it could not look at historical grievances and was largely ineffective in dealing with land issues. The tribunal's own account records that since the treaty was signed in 1840 Māori had made many complaints to the Crown that its terms were not being upheld, and that these petitions and protests often fell on deaf ears. By the early 1980s only seven claims had been investigated. In 1985 the fourth Labour government significantly extended the tribunal's jurisdiction, giving it the power to investigate claims from the signing of the treaty in 1840.

The Treaty of Waitangi Amendment Act 1985 received assent on 9 December 1985 and came into force 28 days later. It allowed any Māori who claimed to be, or to be likely to be, prejudicially affected by an Act or regulation passed on or after 6 February 1840, by a Crown policy or practice, or by anything done or omitted by the Crown on or after that date, and that it was inconsistent with the principles of the treaty, to submit a claim to the tribunal. The Act kept the Chief Judge of the Māori Land Court as the tribunal's chair and required that at least four of the other members be Māori. The tribunal could now commission research on a claim and receive the resulting report in evidence, appoint counsel to assist claimants, and have a registrar and research staff. Its hearings could adopt aspects of te kawa o te marae, but no one could be denied the right to speak because of their sex. The Act also replaced the Māori text of the treaty set out in the 1975 Act.

Soon afterwards the government broke up its old land-holding departments and set up state-owned enterprises under the State-Owned Enterprises Act 1986, which declared that the Crown could do nothing 'that is inconsistent with the principles of the Treaty of Waitangi'. The act also raised the possibility that Crown land subject to treaty claims could pass out of Crown ownership and become unavailable for settlements. In 1987 the New Zealand Māori Council took a case to the Court of Appeal challenging the act. In what became known as the Lands case, the court ruled in the council's favour, characterised the treaty relationship as a partnership, and identified a set of treaty principles the government had to consider before transferring assets to state-owned enterprises. In NZHistory's summary, the case established that the Crown must pay heed to previous Māori ownership when disposing of surplus Crown assets such as land. The decision led to the Treaty of Waitangi (State Enterprises) Act 1988.

The tribunal's higher profile brought a backlash. Some people felt that historic grievances were best forgotten, and the National Party's spokesperson on Māori affairs, Winston Peters, said the tribunal should be downgraded to a research unit that would report to government on the historical facts. In the late 1980s its chair, Eddie Durie, received so many abusive telephone calls that he made his number confidential. Many critics were concerned about the possible cost of settling claims, and some thought it might cripple the economy. Claimants, for their part, were concerned about how long claims took to resolve and that inquiries could pit one iwi or hapū against another. By 1993 there was a backlog of several hundred claims waiting to be heard. The Rangahaua Whanui project, a series of research reports on the main grievances in each district, did not significantly reduce the workload, and in 1995 the tribunal's director, Buddy Mikaere, resigned, expressing frustration at the lack of resources.

In 1996 the tribunal began researching and hearing all the claims in a district together and reporting on them in a single large report, starting with the Mōhaka ki Ahuriri district in Hawke's Bay. In 2008 Parliament removed its power to register new historical claims. By its 40th anniversary in 2015 the tribunal had registered 2,501 claims and issued district reports covering 79% of New Zealand's land area. Te Ara judges that the 1985 change made the tribunal more relevant for the settlement of historical land losses and probably lessened protest about them. The settlement legislation that followed acknowledged the change directly: the preamble to the Ngāi Tahu Claims Settlement Act 1998 records that through the 1985 amendment the Crown 'made it possible for Māori to bring claims before the Waitangi Tribunal in respect of historic grievances arising after 6 February 1840'.