BOISE - Four environmental groups filed a lawsuit late Thursday to prevent a federal agency from extending a wolf- and coyote-hunting derby onto additional public lands in east-central Idaho.

The lawsuit filed in federal court in Idaho came less than two hours after the U.S. Bureau of Land Management approved Idaho for Wildlife's request for the derby permit near Salmon.

Defenders of Wildlife, the Center for Biological Diversity, Western Watersheds Project and Project Coyote say the BLM's actions are contrary to the federal government's wolf reintroduction efforts.

Amy Atwood of the Center for Biological Diversity called the decision "repugnant" and a "slap in the face" to thousands of people who commented against the derby.

She said the BLM "has the authority to make sure wolves are protected and secure on land that's supposed to be a refuge for this fragile population."

BLM officials in approving the permit said the impacts of an estimated 500 hunters on about 3 million acres of BLM land over a three-day period on Jan. 2 to 4 will not be significant.

"We are aware of the social controversy regarding the event," Joe Kraayenbrink, the BLM's district manager in Idaho Falls, said in a statement. "However, from our analysis, we could not find significant conflicts with other environmental resources that would prohibit the competitive event from occurring."

The derby last winter was held on private land and U.S. Forest Service land but not BLM land because Idaho for Wildlife didn't have a permit required by that agency for a competitive event. The BLM permit roughly doubles the hunting area.

"It's wonderful," said Steve Alder of Idaho for Wildlife. "That's going to give us a lot more real estate to hunt on. We expect to get a lot more coyotes, and maybe a wolf or two."

Hunters killed 21 coyotes but no wolves last year. Alder said the addition of the BLM land, which is usually at a lower elevation than Forest Service land, will likely hold more coyotes.

"We have the right and privilege to do this," he said.

The BLM permit the group received Thursday is good for five years, and Alder said he plans to hold an annual coyote and wolf derby. He said his group is prepared for the court challenge.

In 2013, Idaho for Wildlife offered two separate, $1,000 prizes - one for the hunter who killed the biggest wolf, the other for the hunter who bagged the most coyotes. The event drew 230 people, about 100 of them hunters.

Alder said he expected up to 150 hunters this winter, and likely more who would take part in some way but not hunt.