The Dormant Commerce Clause Explained

The Commerce Clause (Art. I, §8) gives Congress power to regulate interstate commerce. The Dormant Commerce Clause (DCC) is the flip side: even when Congress hasn't acted, states cannot pass laws that unduly burden or discriminate against interstate commerce. It's an implied limitation derived from the structure of the Commerce Clause.

Step 1: Does the law discriminate against interstate commerce?

Facially discriminatory: The law explicitly treats in-state and out-of-state interests differently. Apply strict scrutiny — virtually per se invalid unless the state proves no less discriminatory alternatives exist.

Facially neutral but discriminatory in effect: Also subject to heightened scrutiny if the purpose or effect is protectionist.

Step 2: If non-discriminatory, apply the Pike balancing test.
The law is valid unless the burden on interstate commerce is clearly excessive in relation to the putative local benefits (Pike v. Bruce Church).

When a state acts as a market participant (buyer or seller) rather than a regulator, the DCC doesn't apply. The state can prefer in-state businesses when spending its own money or selling state-owned products. Example: A state-owned cement plant can choose to sell only to in-state buyers.

Congress can authorize state laws that would otherwise violate the DCC. If Congress affirmatively allows states to discriminate against interstate commerce, the DCC challenge fails. Congress can also preempt state regulation entirely.

Philadelphia v. New Jersey: New Jersey banned importation of out-of-state waste. Facially discriminatory — struck down.
Pike v. Bruce Church: Arizona required cantaloupes to be packed in-state. Non-discriminatory but unduly burdensome — struck down under balancing.
Dean Milk Co. v. Madison: City required milk to be processed within 5 miles. Discriminatory and less restrictive alternatives existed — struck down.