Ballina police are investigating the site of multiple wallaby deaths on Seven Mile Beach.
Police say as many as 12 of the protected animals have been found dead in the area over the past week, some with obvious bullet wounds.
The discovery comes just weeks after the state government announced that some national parks in the state, including three on the north coast, would be open to shooting of feral animals.
Wallabies were not on the list of permissible animals to be shot and Seven Mile Beach Nature Reserve was not one of the parks opened for shooting.
But wildlife advocates fear that the publicity surrounding the new legislation may have motivated the rampage.
Police believe the shootings are taking place at night or early morning during the week.
Anyone found guilty of shooting the protected species faces a fine of up to $11,000 and/or six months in jail.
Police are continuing to investigate and anyone with information can call Ballina police on 6681 8699 or Crime Stoppers on 1800 333 000.