A citizens’ suit cannot be used to attack the substance of regulations. Such suits are proper when it is alleged that the regulator has failed to fulfill a mandatory duty. It cannot be used to attack a result of discretionary authority given to the administrator. If the agency has failed to meet a statutory deadline or failed to act when Congress has required it to act, then a citizens’ suit is proper.
The plaintiffs in such suits must met Article III standing requirements and must be among those injured by the alleged violation or agency failure.
A proper citizen's suit, for example, might arise in a situation in which a citizen seeks to compel the EPA to promulgate a substitute standard after the EPA has disapproved a state standard and the state has refused to act. CWA § 303(c)(3), 33 U.S.C. § 1313(c)(3).