The Trump administration on Monday finalized changes to the U.S. Endangered Species Act, the 1970s-era wildlife protection law credited with bringing species - including bald eagles, gray whales and grizzly bears - back from the brink of extinction.
The White House and other Republicans say the changes will modernize the law.
Conservation groups say they'll threaten at-risk species.
The Endangered Species Act has long been a source of frustration for drillers, miners and loggers who want to work on land that's off-limits to development.
The law said officials were not supposed to factor in the economic costs - for instance, the loss of development - when it came to safeguarding threatened habitats.
But Monday's changes are meant to let officials factor in economic interests.
Wyoming Republican Senator John Barrasso said the changes were a good first step but that Congress should go further and turn the federal responsibility of protecting animals over to the states.
The weakening of the Endangered Species Act is just one of many moves by the Republican president to roll back regulations to benefit industry.
Conservationists and environmentalists said they would challenge the revised law in court.