“In A.L.A. Schechter Poultry Corp. v. United States, 295 U.S. 495, 550, 55 S.Ct. 837, 851-52, 79 L.Ed. 1570 (1935), the Court struck down regulations that fixed the hours and wages of individuals employed by an intrastate business because the activity being regulated related to interstate commerce only indirectly. In doing so, the Court characterized the distinction between direct and indirect effects of intrastate transactions upon interstate commerce as ‘a fundamental one, essential to the maintenance of our constitutional system.’ Id., at 548, 55 S.Ct., at 851. Activities that affected interstate commerce directly were within Congress’ power; activities that affected interstate commerce indirectly were beyond Congress’ reach. Id., at 546, 55 S.Ct., at 850. The justification for this formal distinction was rooted in the fear that otherwise ‘there would be virtually no limit to the federal power and for all practical purposes we should have a completely centralized government.’ Id., at 548, 55 S.Ct., at 851.” C.J. Rehnquist, United States v. Lopez, 514 U.S. 549, 554-555 (1995).