Fish & Game New Zealand is challenging a new law designed to open more areas to public walking access.
The law establishes a new commission to take over from the Department of Conservation in creating and supervising walkways.
Fish & Game has filed papers in the High Court seeking clarification over whether pastoral leases give land owners exclusive occupancy.
If they are found to do so, anglers and hunters might not be able to access properties on pastoral leasehold land.
Federated Farmers says the lobby group is trying to undermine the new law, despite having been part of the legislative process.
Federated Farmers' spokesperson for access issues, Donald Aubrey, is critical of Fish and Game's decision.
"In my view this action being taken by Fish & Game's chief executive Bryce Johnson is an attempt not only to bully high country farmers into accepting 'wander at will', but also it flies in the face of the very consultative process he was a party to."
But Fish & Game says it is simply standing up for the rights of anglers and hunters.
Mr Johnson says recent public policy and legal research suggests pastoral leases do not include exclusive occupancy.
"All we're doing is simply having the courts clarify that to get beyond all the rhetoric and emotive talk that's been around for many years."
The case is due to be heard at the end of October.