Former Labour Maori Affairs Minister Parekura Horomia says the Government's partial assets sale programme is a confiscation of Maori rights to New Zealand's water.
Labour is urging the Government to delay the sale of shares in the energy company Mighty River Power until the Maori claim over water is settled.
The Waitangi Tribunal is holding an urgent hearing on Maori claims to water, brought by the Maori Council.
Mr Horomia says in selling 49% of shares in state companies with hydro projects, the Government is trying to sell water like it is a commodity.
He says water is something that has been enjoyed by all New Zealanders for generations.
But Maori Party co-leader Tariana Turia has dismissed Mr Horomia's comments, saying he should have thought about that during the foreshore and seabed debate.
The Waitangi Tribunal will hear closing submissions in the water rights hearing on Thursday.