Article I, Section 8, Clause 3 lets Congress "regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes." Read with the Necessary and Proper Clause, it has become the source of much of modern federal law, and its limits are still argued.
Why it works
The arguments turn on one question: what counts as commerce "among the several States"? In Gibbons v. Ogden (1824) Marshall read it broadly: commerce includes navigation, so a federal coasting license beat New York's steamboat monopoly. From the 1890s to 1937 the Court drew lines (manufacturing is not commerce; local activity is for the states). Then, from 1937, it accepted regulation of any activity that, taken together, substantially affects interstate commerce: in Wickard v. Filburn (1942), wheat a farmer grew for his own animals, because millions of such farmers together affect the national market. In United States v. Lopez (1995), 5–4, the Court finally set a limit: carrying a gun near a school is not economic activity, and if it counted, Congress could regulate almost anything. Lopez named three things Congress may regulate: the channels of commerce, its instrumentalities (and people and things in it), and activities that substantially affect it.
Key idea
Congress may regulate commerce "among the several States." The Court read the power broadly (Gibbons, 1824; the New Deal cases; Wickard, 1942), then set limits in United States v. Lopez (1995), which struck down a federal ban on guns near schools.
Worked example: Applying Lopez
A federal law bans selling counterfeit car parts to buyers in other states. Within the commerce power?
- Selling goods across state lines is commerce, and the law regulates things moving in it.
- That is the core of the power, not a stretch.
Answer: Yes.
Worked example: The hard case
A federal law makes it a crime to carry a gun within 1,000 feet of a school. What did the Court hold, and why?
- The government argued guns near schools hurt education and so, in the end, the economy.
- The majority said that chain would let Congress regulate anything; possession of a gun near a school is not economic activity.
- Four justices dissented, arguing Congress could rationally find a substantial effect on commerce.
Answer: Unconstitutional (Lopez, 1995, 5–4): not economic activity that substantially affects interstate commerce.
Common mistake
Thinking the Commerce Clause covers only goods crossing a state line. Since the 1940s it has covered activities that, taken together, substantially affect interstate commerce, even local ones (Wickard, Raich), with the limits Lopez and Morrison set for non-economic activity. Check: ask whether the activity is economic and whether, taken together across the country, it affects a national market.