In a delegation challenge, the constitutional question is whether the statute has delegated legislative power to the agency. Article I, §1, of the Constitution vests "[a]ll legislative Powers herein granted ... in a Congress of the United States." This text permits no delegation of those powers, Loving v. United States, 517 U. S. 748, 771 (1996); see id., at 776-777 (Scalia, J., concurring in part and concurring in judgment), and so we repeatedly have said that when Congress confers decisionmaking authority upon agencies Congress must "lay down by legislative act an intelligible principle to which the person or body authorized to [act] is directed to conform." J. W. Hampton, Jr., & Co. v. United States, 276 U. S. 394, 409 (1928). We have never suggested that an agency can cure an unlawful delegation of legislative power by adopting in its discretion a limiting construction of the statute.
Whitman v. American Trucking Associations, Inc., 531 U.S. 457 (2001).