Diageo American Supply, Inc. (defendant) operated a warehouse. Owners and renters of nearby properties (plaintiffs) complained of whiskey fungus on their properties as a result of Diageo’s warehouse operations. The plaintiffs brought suit in federal district court, seeking damages for nuisance, among other claims, and an injunction ordering abatement of the emissions. Diageo filed a motion to dismiss, arguing that the Clean Air Act preempted the plaintiffs’ state common law claims. The act included a savings clause, affirming the rights of states to adopt or enforce any requirement on emissions if the requirement was at least as strict as those in the act. The district court denied Diageo’s motion. Diageo appealed.