Fish & Game says proposed changes to the Resource Management Act could put trout and salmon habitats in jeopardy.
An independent group appointed by the Government has reviewed several sections in the Act.
But Fish & Game has questioned its definition of sustainable management of natural resources, and methods outlined for doing so.
Nelson and Marlborough manager Neil Deans, said the way the sections have been reworded makes the Act less clear and removes wording specifically calling for the protection of trout and salmon habitats.
He fears the changes will make it easier for natural resources to be over-used.