A state violates the Dormant Commerce Clause if it “oversteps” its role in regulating interstate commerce. The first step in analyzing a state regulation under the Dormant Commerce Clause is to determine whether the regulation incidentally burdens interstate commerce or affirmatively discriminates against interstate commerce. An affirmative burden on interstate commerce exists if the regulation “on its face” or “in its practical effect” regulates interstate commerce.
An incidental burden violates the Commerce Clause only if the burdens it imposes on interstate trade are “clearly excessive in relation to the putative local benefits.” If an affirmative burden is found, the state has the burden to demonstrate that the statute “serves a legitimate local purpose” and that this purpose could not be well served by any available nondiscriminatory means. An affirmative burden is analyzed under strict scrutiny.
State laws that affirmatively discriminate against out-of-staters are almost always declared unconstitutional. Such a law will be allowed only if it is proven that the law is necessary and the least restrictive means were used to achieve a non-protectionist purpose. The only case to survive strict scrutiny under the Dormant Commerce Clause is Maine v. Taylor, 477 US 131 (1986).
If a law does not discriminate against out-of-staters, the Court balances its burdens on interstate commerce against its benefits.