A group of wild horse advocates has filed suit that challenges the Bureau of Land Management’s (BLM) alleged plan to sterilize animals in the Saylor Creek Herd Management Area, located south of Glenns Ferry, Idaho.

In 2014, the BLM announced it would revise its Jarbridge Resource Management Plan of 2010, essentially a blueprint for how the agency would maintain and improve resources including wild life residing in the region including the Saylor Creek wild horses. The revised plan was approved in September 2015.

Some wild horse advocates claim the revised plan calls for the chemical or physical sterilization of the horses in that herd.

On Jan. 4 a group of wild horse advocates—the American Wild Horse Preservation Campaign, The Cloud Foundation, Return to Freedom, and Virginia Marie Hudson—filed a complaint in Idaho District Court alleging that the BLM’s plan violates the National Environmental Policy Act and the Wild Free-Roaming Horses and Burros Act of 1971, the latter of which protects wild horses and burros and places them under the BLM’s jurisdiction. Specifically, the complaint alleges that sterilization would alter the herd’s behavior and could serve as a precedent for herd management plans elsewhere