A refinery in New Mexico that the federal government has accused of some of the worst air pollution in the country.

A chemical plant in Louisiana being investigated for leaking gas from storage tanks.

Idaho ranchers accused of polluting wetlands.

Under President Joe Biden, the Environmental Protection Agency took a tough approach on environmental enforcement by investigating companies for pollution, hazardous waste and other violations. Donald Trump’s administration, on the other hand, has said it wants to shift the EPA’s mission from protecting the air, water and land to one that seeks to “lower the cost of buying a car, heating a home and running a business.”

As a result, the future of long-running investigations like these looks precarious. A new EPA memo lays out the latest changes.

EPA enforcement actions will no longer “shut down any stage of energy production,” the March 12 memo says, unless there’s an imminent health threat. It also curtails a drive started by Biden to address the disproportionately high levels of pollution facing poor communities nationwide. “No consideration,” the memo says, “may be given to whether those affected by potential violations constitute minority or low-income populations.”

Those changes, EPA Administrator Lee Zeldin said, would “allow the agency to better focus on its core mission and powering the Great American Comeback.”

David Uhlmann, who led enforcement at the agency under the Biden administration, said the memo amounted to the agency announcing that “if companies, especially in the oil and gas sector, break the law, this EPA does not intend to hold them accountable.”

That would “put communities across the United States in harm’s way,” he said, particularly poorer or minority areas that often suffer the worst pollution.

Molly Vaseliou, a spokesperson for the EPA, said she could not comment on ongoing investigations or cases. The Department of Justice, which has faced its own staff and budget cuts, declined to comment.

Conservatives have argued that EPA regulations have hurt economic growth and investment. “Bold deregulatory action at EPA will unleash American energy and reduce costs for American families,” Grover Norquist, president of Americans for Tax Reform, an anti-tax organization, said in a statement. “The government’s expensive web of overregulation is being unwoven.”

Enforcement cases brought by the Biden administration are still winding their way through courts. On Wednesday, Japanese truck manufacturer Hino Motors pleaded guilty to submitting false emissions-testing data in violation of the Clean Air Act and agreed to pay more than $1.6 billion in fines stemming from a probe first opened by California in 2019.

At the same time, a wider reframing of the purpose of the EPA is underway. The agency was created a half century ago, during the Republican presidential administration of Richard Nixon, with a mandate to protect the environment and public health.

Recently, the Trump administration said it would repeal dozens of the nation’s most significant environmental regulations, including limits on pollution from tailpipes and smokestacks, and protections for wetlands.

In a video posted on the social platform X, Zeldin said his agency’s mission was now to “lower the cost of buying a car, heating a home and running a business.”

Project 2025, a blueprint for overhauling the federal government that was produced by the Heritage Foundation and written by many who are serving in the Trump administration, goes further, seeking to eliminate the EPA office that carries out enforcement and compliance work.

Zeldin has also said he intends to cut the agency’s spending by 65% and eliminate its scientific research arm. Some on-site inspections, a vital part of enforcement investigations, are being delayed or suspended, according to two people who spoke on the condition of anonymity. Investigations related to air pollution were particularly vulnerable, they said.

There has already been one significant reversal. This month the Trump administration dropped a federal lawsuit against Denka Performance Elastomer, a chemical manufacturer accused of releasing high levels of a likely carcinogen from its Louisiana plant.

The Biden administration filed the lawsuit after regulators determined that emissions of chloroprene, used to make synthetic rubber, were contributing to health concerns in a region along the Mississippi River with some of the highest cancer risk in the United States.