In a last-gasp effort before departing the White House, the Trump administration took another swipe at weakening enforcement of a 100-year-old law that protects migrating birds.

With only two weeks left in office, the administration published a rule Tuesday that spares industries and individuals from prosecution or penalties under the Migratory Bird Treaty Act if their actions, such as development or failure to cover tar pits, results in bird deaths. If the deaths were unintentional, the U.S. Fish and Wildlife Service says in the rule, there will be no enforcement.

Conservation groups immediately promised to sue to stop the rule from going into effect a month from now. They also called on the Biden administration to overturn it.

The groups are confident a legal challenge will prevail due to an earlier court decision that rejected the opinion on which the new rule is based.

U.S. District Judge Valerie Caproni issued a blistering opinion in August that quoted Harper Lee’s famous novel, after deciding in favor of state attorneys general and conservationists who sued the administration.

“It is not only a sin to kill a mockingbird, it is also a crime,” Caproni wrote. “That has been the letter of the law for the past century. But if the Department of the Interior has its way, many mockingbirds and other migratory birds that delight people and support ecosystems throughout the country will be killed without legal consequence.”

On its face, the opinion that supported the administration’s rationale for changing the rule, Caproni decided, “is contrary to the plain meaning of the MBTA and therefore must be vacated.”

But the Interior Department, which oversees the U.S. Fish and Wildlife Service, soldiered on with its rulemaking process despite the decision.

In an analysis issued months after Caproni’s ruling, the department said it would not cause unacceptable environmental harm.

“This rule simply reaffirms the original meaning and intent of the Migratory Bird Treaty Act by making it clear that the U.S. Fish and Wildlife Service will not prosecute landowners, industry and other individuals for accidentally killing a migratory bird," said Interior Secretary David Bernhardt.

The administration’s decision to relax enforcement against killing birds, mostly on behalf of the oil and gas industry, followed two major reports that said human activity has triggered the sixth great extinction of wildlife, including the loss of billions of birds in North America.

In May 2019, a United Nations panel determined that 1 million species face extinction — “more than any other period in human history.”

Four months later, top ornithologists in government and academia reported that 3 billion birds have vanished in North America over the past 50 years.

“The historic environmental protections under the Migratory Bird Treaty Act have been upheld for nearly a century," Sen. Chris Van Hollen (D-Md.) said in a statement. “The Trump administration’s new rule renders these safeguards absolutely toothless, and means corporations would no longer be subject to penalties under this landmark environmental law for disasters like the Deepwater Horizon oil spill.”

The American Exploration and Production Council, an oil industry lobby group, supported the rule, saying oil and gas facilities “are much less of a threat to birds.” Companies screen facilities and remove harmful substances from pits, and use nets and fences to cover the pits and prevent birds from plunging in.

“American oil and gas companies use technological innovations and follow all applicable regulations to protect migratory birds," Anne Bradbury, the council’s chief executive, said in a statement. "We fully support the final ‘Migratory Bird’ rule; better defining the scope of the MBTA and its prohibitions provides much-needed clarification of the Congressional intent and acknowledges current industry best practices to protect migratory birds and their habitat.”

Past Fish and Wildlife estimates show that industry sources kill an average of 709 million birds each year, and up to 1.1 billion. Oil pits alone kill up to 1 million birds yearly.

That compares to 1.4 billion birds killed by feral and household cats, and nearly a billion killed in automobile collisions. Nearly 600 million birds fly into glass buildings each year, and power lines electrocute 5.6 million.

The Center for Biological Diversity is one of the groups that promised to sue. "We’re certainly going to challenge this and are confident we will overturn this,” said Noah Greenwald, endangered species director at the center.

The center is part of a coalition of groups that prevailed in the earlier lawsuit, including the Natural Resources Defense Council, the Audubon Society and Defenders of Wildlife.

“The court found that their interpretation is inconsistent with the law, and they just plowed forward anyway," Greenwald said. “It was a paper exercise to try and hold on to something they were already doing. If the courts don’t overturn it, the Biden administration probably will."

Biden selected Rep. Deb Haaland (D-N.M.) to replace Bernhardt at Interior. Haaland, an environmental justice advocate, has frequently criticized President Trump’s environmental policies.

“Americans want birds and nature taken care of — not swept aside to serve commercial interests. We urge the incoming Administration to right this wrong as rapidly as possible,” said Steve Holmer of American Bird Conservancy.

Jim Murphy, director of legal advocacy at the National Wildlife Federation, pointed out that iconic species such as the snowy egret, wood duck and sandhill crane are disappearing at a time when the administration is easing rules to protect them.

“This decision completely fails to comply with the Migratory Bird Treaty Act and will likely result in countless avoidable bird deaths," Murphy said in a statement. “We are calling on the Biden administration and Congress to right this historic wrong by reinstating the act’s protections and taking up the Migratory Bird Protection Act in the 117th Congress.”