Winter can be hard, especially for elk and other animals who lack a constant feed source during extreme conditions. This is why supplemental feeding stations have been set up in places like Wyoming’s National Elk Refuge: to provide alfalfa pellets to elk that may not have another source of food. However, this week, the Sierra Club, National Wildlife Refuge Association and Defenders of Wildlife filed a lawsuit against the U.S. Fish and Wildlife Service, claiming that “the practice encourages disease,” particularly chronic wasting disease (CWD), the San Francisco Chronicle reports.

“The National Elk Refuge is supposed to sustain healthy populations of native wildlife, not spread infection of lethal disease,” said attorney Tim Preso with the environmental law firm Earthjustice, which is representing the environmental groups.

CWD has impacted elk, deer and moose across the nation, resulting in mandatory testing, herd culls and other management strategies to keep the fatal disease from spreading. The lawsuit alleges that by providing this supplemental winter feed in the refuge, it creates an unnatural elk concentration and could cause more issues among healthy animals. According to the San Francisco Chronicle, the groups have filed the lawsuit to make FWS go through with a 2008 commitment “to gradually decrease elk feeding on the refuge in coordination with the Wyoming Game and Fish Department.”

While the refuge didn’t feed elk last winter because conditions weren’t that bad, they did begin the supplemental feeding program this February due to heavy snow. According to the San Francisco Chronicle, roughly 5,000 elk utilized this extra feed. The supplemental feeding program was initially created about 50 years ago to keep hungry elk away from ranching and agricultural operations.