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

Pruitt, the former attorney general of Oklahoma, has charged ahead with efforts to weaken, block or delay a wide array of stricter pollution and public health standards following his appointment by President Donald Trump earlier this year.

Pruitt’s delay of the 2015 ozone standards comes as Republicans in Congress are pushing for a broader rewrite of the rules. A House bill approved last month seeks to delay implementation of the 2015 rules at least eight years. The measure has not yet been brought to a vote in the Senate.

More than a dozen major health organizations oppose the GOP-backed measure, including the National Medical Association, the American Academy of Pediatrics and the American Public Health Association. The head of the American Lung Association called the industry-backed bill a “direct assault” on the right of Americans to breathe healthy air.

Ground-level ozone is created when common pollutants emitted by cars, power plants, oil refineries, chemical plants and other sources react in the atmosphere to sunlight. The National Ambient Air Quality Standards adopted by EPA in 2015 reduced the allowed amount of ground-level ozone from 75 parts per billion to 70 parts per billion.