Ngati Kahungunu Iwi chairman Ngahiwi Tomoana says Ngai Tahu failed to tell him they had already invested in the proposed Ruataniwha water storage scheme.
Ngai Tahu Holdings has signed a memorandum of understanding with Hawke's Bay Regional Investment that the South Island iwi will invest in the scheme once consents had been granted and financial viability confirmed.
The scheme will generate electricity, protect minimum flow levels on the Tukituki River and irrigate up to 30,000ha but opponents say it will pollute the river by intensifying farming.
Mr Tomoana said Ngati Kahungunu would never invest in something that would destroy its taonga and Ngai Tahu had offered to be a mitigating force for any negative effects of the scheme and would withdraw from the investment if asked.
But Mr Tomoana said he did not find out Ngai Tahu had already put money into the scheme until he read a report in Hawke's Bay Today. He said Maori should not have to pay for their rightful share in natural resource development.