Cite as: 532 U. S. 483 (2001)
Opinion of the Court
District Court to enjoin completion of a dam, whose operation would either eradicate the known population of the snail darter or destroy its critical habitat. Id., at 193-195. The District Court lacked discretion because an injunction was the "only means of ensuring compliance." Romero-Barcelo, supra, at 314 (explaining why the District Court in Hill lacked discretion). Congress' "order of priorities," as expressed in the statute, would be deprived of effect if the District Court could choose to deny injunctive relief. Hill, supra, at 194. In effect, the District Court had only a Hobson's choice. By contrast, with respect to the Controlled Substances Act, criminal enforcement is an alternative, and indeed the customary, means of ensuring compliance with the statute. Congress' resolution of the policy issues can be (and usually is) upheld without an injunction.
B
But the mere fact that the District Court had discretion does not suggest that the District Court, when evaluating the motion to modify the injunction, could consider any and all factors that might relate to the public interest or the conveniences of the parties, including the medical needs of the Cooperative's patients. On the contrary, a court sitting in equity cannot "ignore the judgment of Congress, deliberately expressed in legislation." Virginian R. Co. v. Railway Employees, 300 U. S. 515, 551 (1937). A district court cannot, for example, override Congress' policy choice, articulated in a statute, as to what behavior should be prohibited. "Once Congress, exercising its delegated powers, has decided the order of priorities in a given area, it is . . . for the courts to enforce them when enforcement is sought." Hill, 437 U. S., at 194. Courts of equity cannot, in their discretion, reject the balance that Congress has struck in a statute. Id., at 194-195. Their choice (unless there is statutory language to the contrary) is simply whether a particular means of enforcing the statute should be chosen over another per-
497
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