The court has never suggested that an agency can cure an unlawful delegation of legislative power by adopting in its discretion a limiting construction of the statute. Both Fahey v. Mallonee, 332 U. S. 245, 252-253 (1947), and Lichter v. United States, 334 U. S. 742, 783 (1948), mention agency regulations in the course of their nondelegation discussions, but Lichter did so because a subsequent Congress had incorporated the regulations into a revised version of the statute, ibid., and Fahey because the customary practices in the area, implicitly incorporated into the statute, were reflected in the regulations, 332 U. S., at 250. The idea that an agency can cure an unconstitutionally standardless delegation of power by declining to exercise some of that power seems to us internally contradictory. The very choice of which portion of the power to exercise-that is to say, the prescription of the standard that Congress had omitted-would itself be an exercise of the forbidden legislative authority. Whether the statute delegates legislative power is a question for the courts, and an agency's voluntary self-denial has no bearing upon the answer.