Re-flagging foreign charter fishing vessels could cost a Maori body overseeing fisheries quota held by iwi up to $120 million.
Government ministers announced in May a proposed law change to bring the deep sea vessels under New Zealand jurisdiction by 2016.
Maori-owned fishing companies catch about 15% of the deep sea quota annually, using some foreign charter vessels to net their fish.
Te Ohu Kaimoana (Maori Fisheries Trust) says the re-flagging could reduce annual income for iwi quota owners by $10 million if the owners of the vessels no longer want to work in New Zealand waters.
Chief executive Peter Douglas says that drop would be due to the loss of income for the low value fish stocks that cannot be caught by the New Zealand fleet.
He says the price of high value fish such as hoki and orange roughy is likely to drop by about 15% because there will be fewer boats catching deepsea fish and therefore less competition for it.
Maori fishing asset holders now control about 37% of the total fish quota - valued at $4.5 billion.