(Reuters) - Fourteen states filed suit on Thursday accusing the U.S. Environmental Protection Agency of failing to issue regulations for curbing emissions of methane, a potent greenhouse pollutant, from existing oil and gas operations as required under the Clean Air Act.

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The legal challenge, led by New York state, came nine months after a federal appeals court sided with environmental activists who sued to block the EPA from freezing enforcement of its own rules to control methane leaks from new or modified fossil fuel facilities.

In both instances, EPA chief Scott Pruitt has been accused of putting the interests of oil and gas companies ahead of the agency’s obligation to protect air quality, including the control of heat-trapping pollutants that scientists blame for global climate change.

Pruitt, who was a leading EPA critic as attorney general of the oil-producing state of Oklahoma before beginning his tenure as head of the EPA, has said he does not believe greenhouse gas emissions are the principal driver of climate change.

As EPA administrator, Pruitt has moved to carry out U.S. President Donald Trump’s campaign pledge to roll back or reconsider a slew of environmental protections deemed burdensome by the industry, including climate change regulations.

In March 2017 Trump signed an order to undo climate rules. And the EPA that month halted efforts to collect data from fossil fuel operations to prepare performance standards that states would have to follow in devising methane-control measures for existing wells, pipelines, storage tanks, pumping stations and other facilities.

It was EPA’s “unreasonable delay” in developing those standards that Thursday’s lawsuit, filed in U.S. District Court in Washington, cited as a Clean Air Act violation.

“The EPA has a clear legal duty to control methane pollution from oil and gas operations,” New York Attorney General Eric Schneiderman said. “Its continued refusal to do so is not only illegal, but threatens our public health and environment.”

The lawsuit prepared by his office was joined by California, and 12 other states including Illinois, Pennsylvania, New Mexico, Vermont and Iowa, as well as the District of Columbia and the city of Chicago.

Pruitt was named as the sole defendant in the complaint, which seeks a court order compelling the EPA to devise and issue the emissions standards in question.

An EPA spokeswoman said the agency does not comment on pending litigation.

Methane, the main component of commercially distributed natural gas, is also a byproduct of oil extraction. Pound for pound, it traps significantly more heat in the atmosphere than carbon dioxide, the most prevalent greenhouse gas, though its effects are shorter-lived.

The oil and gas industry accounts for nearly third of all U.S. methane emissions, according to an EPA report cited in the lawsuit. The overwhelming bulk of those emissions, equivalent to 328 million metric tons of carbon dioxide each year, come from facilities in existence prior to 2012, the complaint said.

The lawsuit cited an Environmental Defense Fund study that found the industry could cut methane emissions 40 percent below projected 2018 levels at an average annual cost of less than a penny per thousand cubic feet of natural gas produced. The study said that reduction could save the U.S. economy more than $100 million a year.