BOISE, Idaho (AP) — Wild horse advocates have filed a lawsuit challenging a U.S. Bureau of Land Management plan to sterilize a herd of wild horses in southwestern Idaho.

The lawsuit filed Monday in U.S. District Court in Idaho contends the BLM is violating federal environmental law by failing to analyze consequences of the action.

The American Wild Horse Preservation Campaign and two other groups also say the BLM is violating the Wild Free Roaming Horses and Burros Act by adopting a plan that fails to protect wild horses.

The BLM in September released a plan for the Saylor Creek Herd Management Area that calls for wild horses to be sterilized and the herd to be kept between 50 and 200 horses.

The BLM didn't return a call from The Associated Press on Tuesday.