The Maori Council will head to the High Court on Tuesday to argue the government's plan to sell shares in energy companies before it sorts out water rights is illegal.
Maori Council lawyer Donna Hall filed papers at the court late on Friday, and ground rules and timetables for an urgent judicial review will be set in the High Court in Wellington on Tuesday.
The court challenge was launched after the government announced it wouldn't change its plan to sell 49 per cent of energy companies despite a Waitangi Tribunal recommendation that the plan be halted until Maori claims to water are determined.
The first share float - 49 per cent of Mighty River Power - is due to take place between March and June next year.
Ms Hall told NZ Newswire that an urgent hearing date was likely to be set on Tuesday.
She earlier said the council had no option but to mount a legal challenge.
"We will be saying the government is acting illegally if it proceeds to sell the shares before it has sorted out what the Maori interests are in the water that the companies use," she said on Friday.
"It (partial privatisation) may wipe out any ability to define those interests."
The council will also argue that Waikato iwi with interests in the water Mighty River Power uses for hydro generation are still waiting for Treaty of Waitangi claims to be heard.
The council is gathering money from iwi to pay for the High Court challenge.
The government expects the council to take legal action and says it is confident it will win the case because it has fulfilled all its treaty obligations.