Environmental and health groups sued the Trump administration Monday because the Environmental Protection Agency (EPA) missed a key deadline in enforcing a major air pollution rule.

The groups, including Earthjustice, the Sierra Club and the American Lung Association, say the Clean Air Act required the EPA to say which areas of the country are not in compliance with 2015 ozone rule by Oct. 1, but it missed that deadline.

“We cannot stand by as an executive official flagrantly flouts the law. It’s dangerous and corrosive,” Seth Johnson, a staff attorney at Earthjustice, said in a statement.

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“More than half the people in the United States live in a county where EPA has yet to say if air quality meets the strengthened standard. Everyone deserves to breathe clean air. And because of the Clean Air Act, we’re legally entitled to it.”

“We are extremely disappointed but not surprised by Administrator [Scott] Pruitt’s unwillingness to declare the areas in our country that are not meeting ozone standards. Every day that passes, people are exposed to dangerous pollutants,” said Georges Benjamin, executive director of the American Public Health Association.

An EPA spokesman declined to comment on the lawsuit, saying, "the agency doesn't normally comment on pending litigation."

Pruitt fought the rule in his past job as Oklahoma’s attorney general, saying it would be unacceptably expensive for states to reduce their air pollution enough to comply with it.

He tried in June to delay the nonattainment designations for the ozone rule. But, facing lawsuits from greens and Democratic state attorneys general, he walked back that delay.

Then, in November, Pruitt released findings that 2,646 counties, two tribal areas and five territories — or about 85 percent of the nation's counties — meet the requirements of the new rule.

But he declined to disclose which areas do not meet it, promising instead to work with states on the issue.

The 2015 rule set the allowable ground-level ozone concentration at 70 parts per billion, down from 75. Ozone is a byproduct of pollutants emitted from burning fossil fuels, and is linked to various respiratory ailments.

Areas that do not meet the new standard have to draw up plans to clean their air. If the plans aren’t sufficient, the EPA is obligated to step in and write its own plans.

A coalition of Democratic state attorneys general have pledged to sue Pruitt over the delayed designations as well.

The green and health groups filed their lawsuit Monday in the federal District Court for the District of Northern California, based in San Francisco.