Excerpt from United States v. Lopez
First, Congress may regulate the use of the channels of interstate
commerce. See, e.g., Darby, 312 U. S., at 114; Heart of Atlanta Motel,
supra, at 256 (" `[T]he authority of Congress to keep the channels of
interstate commerce free from immoral and injurious uses has been
frequently sustained, and is no longer open to question.' " (quoting
Caminetti v. United States, 242 U.S. 470, 491 (1917)).
Second, Congress is empowered to regulate and protect the
instrumentalities of interstate commerce, or persons or things in
interstate commerce, even though the threat may come only from
intrastate activities. See, e.g., Shreveport Rate Cases, 234 U.S. 342
(1914); Southern R. Co. v. United States, 222 U.S. 20 (1911) (upholding
amendments to Safety Appliance Act as applied to vehicles used in
intrastate commerce); Perez, supra, at 150 ("[F]or example, the
destruction of an aircraft (18 U.S.C. § 32), or . . . thefts from
interstate shipments (18 U.S.C. § 659)").
Finally, Congress' commerce authority includes the power to regulate
those activities having a substantial relation to interstate commerce,
Jones & Laughlin Steel, 301 U. S., at 37, i.e., those activities
that substantially affect interstate commerce. Wirtz, supra, at 196, n.