Fisheries Minister Stuart Nash's decision to allow East Coast tarakihi stocks to remain overfished is "not environmentally sustainable or legal", according to Forest & Bird.
The conservation organisation is set to argue at a High Court hearing in Wellington that East Coast tarakihi stock has been fished down to 15 per cent of their natural population.
Fisheries NZ previously stated that the minimum level that the stock should be fished down to is 40 per cent.
Forest & Bird Chief Executive Kevin Hague said Nash's decision to reduce the commercial catch by 10 per cent in 2019 means it'll take 25 years for the stock to rebuild.
"There is clear Government policy that any fish that is depleted to this extent must be allowed to rebuild, and in the case of tarakihi within 10 years," he said.
"The East Coast tarakihi population has been pillaged to a critically low level. Yet the purpose of the Quota Management System and the Fisheries Act is to prevent this from happening."
Hague said the Napier MP's decision should concern anyone who makes their living from the sea, recreational fishers, and tangata whenua.
"Tarakihi are a key coastal species on which jobs and the health of our coastal seas depend," he said.
"The Fisheries Act is far from perfect, and Forest & Bird believes it needs a significant overhaul to bring fisheries management into the 21st century. But even under the current system, fish stocks should be managed sustainably."
The East Coast tarakihi area in question covers the entire eastern side of the North Island.
Stuart Nash said: "It is inappropriate to comment now that a matter is before the court."
The High Court hearing was due to take place this week.
Forest & Bird also has concerns the Fisheries Minister relied on a voluntary plan provided by the fishing industry which contains actions such as further research, and rules where commercial fishing boats would temporarily move on from an area if they are catching too many undersized fish.
"The Industry Rebuild Plan shouldn't be used in place of an appropriate catch limit. There is no way to determine what impact the industry plan will have, because the plan is voluntary," Hague said.
"Fisheries NZ's advice was that they aren't sure whether the Industry Rebuild Plan will deliver an accelerated rate of rebuild."
More than 90 per cent of the tarakihi caught are sold locally, according to Forest & Bird.