Montana state officials have already made a New Year’s resolution: Sue the federal government. In a lawsuit filed on Dec. 31, Montana Governor Greg Gianforte accused the U.S. National Park Service (NPS) of violating established agreements for managing bison.

Federal wildlife officials have ignored Montana’s concerns about increased numbers of bison, the lawsuit said, and also avoided vaccinating the animals against brucellosis, a disease that worries the state’s cattle-ranching industry.

It’s the latest escalation in a decades-long conflict between state and federal officials over management of bison herds in Yellowstone National Park. The core issue is about how to manage the animals when they leave park borders and roam into Montana. According to the lawsuit, the NPS changed the rules regarding bison numbers and vaccination in a 2024 environmental impact statement without consulting state officials.

The lawsuit was filed in district court by Gianforte’s office, the Montana Department of Livestock, and the Montana Department of Fish, Wildlife, and Parks. The NPS didn’t immediately respond to requests for comment on Thursday.

“The new Bison Management Plan is another example of Yellowstone National Park’s tendency to do what it wants, leaving Montana to collect the pieces,” the lawsuit said.

Is Livestock Disease the Issue?

The latest dispute began in 2000 when Yellowstone National Park implemented the Interagency Bison Management Plan. This long-term plan allowed for brucellosis-positive bison to live in Yellowstone. That concerned Montana officials because brucellosis can cause fetal abortion and sterility in livestock, and Yellowstone bison frequently roam outside of park boundaries.

State officials hoped the issue would be addressed when the NPS updated the management plan in July 2024. But that’s not what happened, according to the lawsuit. Instead, the updated plan violates previous agreements to keep bison Yellowstone bison herds under 3,000 animals, and avoids vaccinating them against brucellosis, Gov. Gianforte said in a July 2024 letter to federal officials.

“The condescending and disingenuous methods of NPS, and other agencies, is forcing a new day in the West,” Gianforte wrote.

While brucellosis has been found among Yellowstone bison, it’s more likely to infect livestock via elk herds, according to 2016 research from the U.S. Geological Survey.

“Any attempt to control the rate of spread in wildlife must be evaluated at the ecosystem scale and include an effective strategy to address infection in elk across the greater Yellowstone area. Focus on bison alone, as was suggested in the past, will not meet the disease eradication objective and conserve wildlife,” said the National Park Service’s Rick Wallen, lead wildlife biologist for the bison program in Yellowstone National Park and co-author of the 2016 study.

Too Many Bison?

But by 2023, the Yellowstone bison population had swelled to 6,000, or double the intended herd limit from the 2000 plan. That led to Montana hunters killing many of the animals at point-blank range as they wandered outside park borders, according to conservation groups Roam Free Nation and Alliance for the Wild Rockies.

“The so-called ‘hunt’ is just another tool to achieve what livestock interests want — to keep wild bison out of Montana,” the organizations said jointly in a press release.

Regardless, the Montana lawsuit requests a temporary pause of the 2024 bison plan while the court reviews the state’s claims.