The Ministry of Fisheries is cracking down on what it calls "greedy" paua poachers who are taking large amounts of paua in the Coromandel town of Tairua.
Three men face prosecution, accused of catching 14 times their daily quota.
The limit is 10 paua per person a day, but the ministry claims the trio took a total of 420 paua. All were undersized.
Coromandel operations manager Brendon Mikkelsen says five other people were caught several days ago with 108 paua. All of these were undersized.
Mr Mikkelsen says the ministry is increasing patrols in the area and encouraging people to report poachers.