The Environmental Protection Agency rule would have made it easier for utilities, refineries and other industrial facilities to make repairs in the name of "routine maintenance" without installing additional pollution controls.
A three-judge panel of the U.S. Circuit Court of Appeals for the District of Columbia issued an order that blocks the rules from going into effect until the legal challenge from the states and cities is heard, a process likely to last months.
The court's decision blocks at least temporarily one of the Bush administration's major environmental decisions. The court's justices said the challengers "demonstrated the irreparable harm and likelihood of success" of their case, which are required to stop the rule from taking effect.
EPA proposed the rule in December, the then-acting administrator signed it in August and it was made final in October. It was due to have gone into effect this week.
Bringing suit were attorneys general for 12 states — Connecticut, Maine, Maryland, Massachusetts, New Hampshire, New Mexico, New Jersey, New York, Pennsylvania, Rhode Island, Vermont and Wisconsin — and legal officers for New York City, Washington, San Francisco, New Haven and a host of other cities in Connecticut.
There was no immediate comment available from EPA officials.
EPA has maintained that it does not believe the rule will result in significant changes in emissions, and that it will preserve the public health protections required under law.
Environmental and health groups, including Natural Resources Defense Council and the American Lung Association, also challenged the rule in the appeals court.
They argued EPA's maintenance rule violates the Clean Air Act by letting power plants and other industries increase pollution significantly without adopting control measures, and public harm would result.
"This is a great gift to the American people and a lump of coal to the Bush administration and its polluter friends," John Walke, NRDC's clean air director. "The court agreed this rule would cause great harm to the public that could not be undone, and it's likely the rule will be struck down for running afoul of the Clean Air Act."