Under the Clean Air Act, factories and other facilities that release large amounts of toxic air pollution are classified as "major sources" and must meet strict pollution-control rules. The EPA had issued a rule saying that if one of these facilities downgrades to a smaller "area source" category — which faces looser pollution limits — it still has to keep using the same pollution-control equipment so its emissions don't actually increase. This resolution cancels that EPA rule, meaning facilities that reclassify as smaller sources would no longer be required to keep those stricter controls in place just to prevent a rise in emissions of pollutants that can build up in the environment and in people's bodies over time.