The rules, part of the Clean Air Act of 1970, are known as new source review, and apply to old plants that were exempted from meeting new pollution standards.

The provision in question is known as new source review.

At issue is a provision of the Clean Air Act known as new source review.

The provision, known as new source review, compels utilities to install modern pollution controls whenever they build a new power plant or significantly upgrade or expand one already in use.

The power companies strongly objected to the rules, which were known as "new source review," calling them arbitrary, expensive and outmoded.

The main retreat involved a section of the Clean Air Act known as "new source review."

The provision, known as "new source review," requires older power plants to install modern pollution-control equipment whenever they significantly expand production.

That stand, proposed as a federal rule, would affect a part of the Clean Air Act known as new source review, which was intended to accelerate the phase-out of the old plants.

The amendment became known as "new source review" because it required review when a plant added new power sources that could raise emissions.

The second proposal would gut a key provision of the Clean Air Act known as "new source review."