Chatham Rock Phosphate has applied for marine consent to mine phosphate 450 kilometres east of Christchurch.
Iwi in the rohe - Ngai Tahu, Ngati Mutunga O Wharekauri and the Hokotehi Moriori Trust - have said if the mining is approved, it would have a destructive effect on an important breeding ground and on commercial fish species.
Ngati Porou Seafoods chief executive Mark Ngata agreed and said the company was backing the iwi.
Chatham Rock Phosphate said in its submission to the Environmental Protection Authority that it would take measures to protect the environment and any potential impact on it, or fish, would be minor.
Sealord Fishing general manager Doug Paulin, of Ngati Porou, disagreed and said it should not be touched.
Mr Paulin said it was in an area where Sealord had ceased operations for a number of years and in a protected area that it did not trawl through.
He said it was like a national park at sea and Sealord saw the strip-mining of it as something the company did not want to support. The risks to the environment were too great, he said.
Whanganui Fisheries Limited operations manager Ben Potaka said the Whanganui iwi was astonished when it found out what Chatham Rock Phosphate was proposing.
"We have put in a submission opposing the mining. I watched Chatham Rock Phosphate's own promotional video on its mining plans and it showed the extent of the damage it would cause. It showed an unbelievable amount of destruction to the environment."
Mr Potaka said Chatham Rise was an important breeding ground for species such as hoki and ling.
Chatham Rock Phosphate said its plan for mining was technologically robust, environmentally sound, economically attractive, socially responsible and based on scientific research and consultation with stakeholders.