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symmetry cannot trump an asymmetrical statute." CSX Transp., Inc. v. Alabama Dept. of Revenue, 562 U. S. 277, 296 (2011).

EPA persists that Congress treated power plants differently from other sources because of uncertainty about whether regulation of power plants would still be needed after the application of the rest of the Act's requirements. That is undoubtedly one of the reasons Congress treated power plants differently; hence §7412(n)(1)(A)'s requirement to study hazards posed by power plants' emissions "after imposition of the requirements of [the rest of the Act]." But if uncertainty about the need for regulation were the only reason to treat power plants differently, Congress would have required the Agency to decide only whether regulation remains "necessary," not whether regulation is "appropriate and necessary." In any event, EPA stated when it adopted the rule that "Congress did not limit [the] appropriate and necessary inquiry to [the study mentioned in §7412(n)(1)(A)]." 77 Fed. Reg. 9325. The Agency instead decided that the appropriate-and necessary finding should be understood in light of all three studies required by §7412(n)(1), and as we have discussed, one of those three studies reflects concern about cost.

The dissent does not embrace EPA’s far-reaching claim that Congress made costs altogether irrelevant to the decision to regulate power plants. Instead, it maintains that EPA need not “explicitly analyze costs” before deeming regulation appropriate, because other features of the regulatory program will on their own ensure the costeffectiveness of regulation. Post, at 2 (opinion of KAGAN, J.). This line of reasoning contradicts the foundational principle of administrative law that a court may uphold agency action only on the grounds that the agency invoked when it took the action. SEC v. Chenery Corp., 318 U. S.