SALMON, Idaho Conservationists threatened to sue on Friday in order to block a plan by U.S. wildlife managers that strips grizzly bears of federal protection, opening them to hunting around Yellowstone National Park.

Three coalitions – the Humane Society, WildEarth Guardians and another that includes the Sierra Club and the Northern Cheyenne Tribe – each formally notified Republican President Donald Trump’s administration that they intend to file lawsuits to prevent the delisting of the bears as endangered species.

“Truly recovering grizzly bears requires more than making Yellowstone into a proverbial zoo,” said WildEarth Guardians carnivore advocate Kelly Nokes in a statement. “Bears need protections across their range.”

An Interior Department official said in a statement on Friday that the agency had not yet received notices of possible litigation. A request for comment was referred to the Justice Department, which declined to comment.

Last week, U.S. Interior Secretary Ryan Zinke, a former Montana congressman, said Yellowstone-area grizzlies would be removed from the list of endangered species this summer, a move he hailed as “one of America’s great conservation successes” due to the animals’ rebounding population.

The delisting plan, scheduled to go into effect at the end of July, was initially proposed during Democratic President Barack Obama’s administration.

The number of grizzlies in the greater Yellowstone region has climbed to roughly 700 from 136 in 1975, when the bears in the Lower 48 states were formally listed as threatened after being hunted, trapped and poisoned to near-extinction. The current total exceeds the government’s minimum recovery goal of 500 animals in the region.

Despite those gains, the grizzly is found in only about 2 percent of its original range in the Lower 48 states.

Delisting the bears is strongly supported by hunters, who prize them as trophy animals, and ranchers, a powerful political constituency in the region who say the bears’ growing numbers pose a threat to humans and livestock.

Environmentalists, meanwhile, argue that while the grizzlies have made a comeback, their recovery could falter without federal safeguards.

The groups on Friday said they had sent Zinke letters that they will sue the Interior Department in 60 days unless the government abandons the delisting plans. They contend that habitat loss due to livestock grazing and timber harvesting, as well as dwindling food supplies due to climate change, were not accurately assessed by federal officials in making the decision.

Yellowstone National Park is mostly in Wyoming but spreads into parts of Montana and Idaho as well.

(Editing by Taylor Harris and Matthew Lewis)