The Ngaruahine iwi in Taranaki is worried about the threat to its fisheries and ocean if an application to mine the seabed is granted.
Trans-Tasman Resources wants to mine iron ore from 65 square kilometres of seabed, 22km off the coast of Patea.
The iwi filed its opposing submission just before feedback closed on Tuesday.
Ngaruahine chairperson Daisy Nobel says if the 20-year application is granted, the iwi believes the life and health of the ocean would be set back for decades afterwards.
She says on a scale of one to 10, the threat to its fisheries and ocean sits at a 10, which is not acceptable.
Ms Nobel says as customary owners, the iwi has set out how the environment should be managed through its kawa (customs).