A coalition of wildlife conservation groups on Thursday formally filed a federal lawsuit against the U.S. Fish and Wildlife Service move that has stripped gray wolves of Endangered Species Act protection across nearly all the lower 48 states.

Six conservation groups represented by Earthjustice — the Center for Biological Diversity, Defenders of Wildlife, Sierra Club, Oregon Wildlife, National Parks Conservation Association and the Humane Society of the United States — filed the 25-page suit in California's northern district federal court.

The federal move to delist wolves, first reported in the News Tribune on Oct. 28, took effect Jan. 4, handing control of the carnivores back to state and tribal resource agencies.

Read more stories about wolves here.

But the groups say the government's actions are premature and too broad, saying wolves are still "functionally extinct" across the vast majority of their original range across the continental United States.

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Wolves received federal protections in 1975 when only about 500 remained in the Lower 48, all of them in Northeastern Minnesota. There are now about 6,000 wolves in the Lower 48, including about 2,700 in Minnesota, more than 1,000 in Wisconsin and more than 500 in Michigan's Upper Peninsula. The animals were delisted in 2011, but a court order put them back under federal protection in late 2014, where they stayed until last week.

Livestock groups and some hunting organizations said the time is long past to begin culling wolf numbers. But the groups said allowing states to manage the animals, including allowing baiting and trapping, threatens to reduce their numbers again.

The suit claims that removal of the gray wolf's federal protection is unlawful because the species has not recovered in the Pacific Northwest, the southern Rockies and elsewhere that scientists identify as "significant" habitat for the wolf.

“The delisting we've challenged today represents the latest chapter in the sad saga of the Fish and Wildlife Service's failure to do its duty to protect and ensure the recovery of wolves under the Endangered Species Act,” Nicholas Arrivo, managing attorney for the Humane Society of the United States, said in a statement Thursday. “We're confident that the court will strike down this illegal decision and restore the federal protections needed to give America's wolves a genuine opportunity to recover.”

The suit also asserts that the Fish and Wildlife Service's decision contradicts the most current science regarding wolf conservation and taxonomy and ignores concerns raised in peer reviews by the nation's top wolf scientists.