In July, the U.S. Appeals Court for the District of Columbia Circuit threw out the Clean Air Interstate Rule, which required 28 mostly Eastern states to reduce smog-forming and soot-producing emissions that can travel long distances in the wind.

The court said the EPA overstepped its authority by instituting the rule, citing "more than several fatal flaws" in the regulation. However, a three-judge panel decided to reinstate the rule while the EPA develops a new clean air program.

Judge Judith W. Rogers said allowing the country to go without the protection of CAIR while the EPA fixes it "would sacrifice clear benefits to public health and the environment."

The judges did not give EPA a deadline to come up with new regulations, but warned the agency that this decision is not an "indefinite stay" of its July ruling.

The Environmental Protection Agency had predicted that the Clean Air Interstate Rule would prevent about 17,000 premature deaths a year by dramatically reducing sulfur dioxide and nitrogen oxide emissions. In addition, the EPA said the rule would save up to $100 billion in health benefits, eliminate millions of lost work and school days and prevent tens of thousands of nonfatal heart attacks.