BILLINGS, Mont. (AP) — Wildlife advocates on Wednesday asked a U.S. judge to force the government into deciding if the snow-loving wolverine should be federally protected as the rare predator becomes vulnerable to a warming planet.

The request comes in a lawsuit filed in Montana almost four years after U.S. District Judge Dana Christensen ordered wildlife officials to take swift action to protect the animal.

Wolverines, also known as “mountain devils." need deep snows to den. Scientists warn such habitat could shrink as the Earth heats up.

Once found throughout the Rocky Mountains and in California’s Sierra Nevada mountains, wolverines were wiped out across most of the U.S. by the 1930s following unregulated trapping and poisoning campaigns.

An estimated 250 to 300 wolverines survive in remote areas of Montana, Wyoming, Idaho, Oregon and Washington state, according to wildlife officials. Populations also are in Canada and Alaska.

Wednesday's lawsuit was filed by attorneys for the Center for Biological Diversity, Defenders of Wildlife and more than a half dozen other groups. The case was assigned to Christensen.

In the judge's April 2016 order, he chastised government officials for rejecting the views of many of its own scientists when it decided not to protect wolverines in 2014. The judge declared in his order that “the time is now” to protect a species “squarely in the path of climate change."

But in a Feb. 28 letter to an attorney for the plaintiffs in the lawsuit, a senior U.S. Fish and Wildlife Service official said “the court did not set a time frame” for a decision.

A final determination on whether the wolverine should be protected is expected by late summer 2020, U.S. Fish and Wildlife Service Deputy Assistant Director Gina Shultz said in the letter to Earthjustice attorney Amanda Galvan.