Armed US rangers are rounding up cattle on federal land in Nevada in a showdown with a rancher who has grazed his herd on public land for decades.
The Center for Biological Diversity told the Bureau of Land Management in 2012 that it intends to sue to protect a tortoise whose habitat in the Mojave Desert was being destroyed by grazing cattle.
Rancher Cliven Bundy stopped paying grazing fees in 1993 on a 600,000 acre allotment of federal range and park land in southern Nevada.
He has also defied federal court orders to remove his cattle, according to the bureau. But the federal government has taken more than 20 years to intervene.
Wranglers have so far seized 277 head of Bundy cattle, many of them cow-calf pairs that may ultimately be sold at auction.
Mr Bundy and his allies liken the dispute to a range war with a remote government seeking to suppress the independent spirit of the West.
"It's a freedom issue that we're really fighting here, and it's bigger than our cows and bigger than the tortoises. It's about the federal government wanting control to do whatever it wants to do," Mrs Carol Bundy said in an interview.