The ranchers claim the culling program violates the National Environmental Policy Act because it fails to take into account environmental effects, the Ashland (Ore.) Daily Tidings reported.
The Oregon Department of Fish and Wildlife has contracted with the U.S. Department of Agriculture to kill up to 66 cougars in three target areas to help determine whether killing the big cats will help protect humans and livestock, the newspaper reported.
Brian Vincent, a spokesman for Big Wildlife of Williams, Ore., one of the lawsuit's plaintiffs, said in a statement Oregon has enlisted the federal government "to do some of its dirty work."
"Their plan is to slaughter cougars across the state using state and federal agents and hunters with hounds. Yet, the plan is based on nothing more than junk science, urban myth and hysteria," Vincent said.
State Sen. Alan Bates, D-Ashland, said the state's thinning of the cougar population pales next to the number killed annually by sport hunters.
"I'd rather have the state doing a careful management plan other than random killing by hunters," Bates said.