The Trump administration on Monday finalized changes to provisions of the U.S. Endangered Species Act that it says will streamline the decades-old wildlife protection law, although conservation groups say it will threaten at-risk species.

The 1970s-era act is credited with bringing back from the brink of extinction species such as bald eagles, grey whales and grizzly bears. However, the law has long been a source of frustration for drillers, miners and other industries because new listings can put vast swathes of land off limits to development.

The weakening of the act's protections is one of many moves by President Donald Trump, a Republican, to roll back existing regulations to hasten oil, gas and coal production, as well as grazing and logging on federal land.

The changes were announced by the Interior Department's U.S. Fish and Wildlife Service and the Commerce Department's National Marine Fisheries Service.

"The revisions finalized with this rulemaking fit squarely within the president's mandate of easing the regulatory burden on the American public, without sacrificing our species' protection and recovery goals," U.S. Secretary of Commerce Wilbur Ross said in a statement.

According to the revision, the Fish and Wildlife Service would need to write separate rules for each threatened species, slowing their protection until conditions worsen. Previously, threatened species, which account for 20 per cent of listed species under the act, would receive the same automatic protections as endangered species, according to the liberal Center for American Progress policy research organization.

The changes would also strike language that guides officials to ignore economic impacts of how animals should be safeguarded. The original act protected species regardless of the economics of the area protected.

Conservationists and environmentalists said they would challenge the revised law in court.

"These changes crash a bulldozer through the Endangered Species Act's lifesaving protections for America's most vulnerable wildlife," Noah Greenwald, director of endangered species with the Center for Biological Diversity, said in a statement.

"For animals like wolverines and monarch butterflies, this could be the beginning of the end."

He said the group would go to court to block the rewritten regulations, "which only serves the oil industry and other polluters who see endangered species as pesky inconveniences."

Democratic Sen. Tom Udall of New Mexico also criticized the plans.

"At a time when one million species are at risk of extinction caused by humans, we should be strengthening the Endangered Species Act, not crippling it," said Udall. "This is wrong and dangerous."

Some lawmakers from Western states and free market conservation groups see them as helping states and landowners. Sen. John Barrasso, Republican from Wyoming, said the revision was a good first step but Congress should also reform the Endangered Species Act.

"We must modernize the Endangered Species Act in a way that empowers states, promotes the recovery of species, and allows local economies to thrive," Barrasso said.

The new rules will also prohibit designation of critical habitat for species threatened by climate change, the Center for Biological Diversity said. Trump rejects mainstream climate science.

Conservation groups and attorneys general of several states including California and Massachusetts had been critical of the changes first proposed last year, saying they were in violation of the purpose of the Endangered Species Act and the National Environmental Policy Act.