The U.S. Supreme Court case Austin et al. v. New Hampshire et al., 1974, revolved around a tax dispute between the state of New Hampshire and non-resident commuters from neighboring states who worked in New Hampshire but lived elsewhere. The State had imposed an income tax only on these non-residents while exempting its own residents from this taxation, which was challenged by the plaintiffs as discriminatory and unconstitutional under both the Privileges and Immunities Clause of Article IV and the Commerce Clause of the U.S Constitution. In a unanimous decision, Justice Potter Stewart delivered the opinion that such differential treatment indeed violated both clauses mentioned above because it placed an unfair burden on interstate commerce by taxing out-of-state residents more heavily than in-state ones for performing substantially similar work within its borders; also it denied them equal protection rights guaranteed to all citizens regardless their state residency status. This ruling effectively invalidated New Hampshire's commuter income tax law, establishing that any form of economic discrimination against out-of-state workers is constitutionally impermissible unless justified by significant differences related to public interest or policy.

In the dissenting opinion for Austin et al. v. New Hampshire et al., the justice argued that New Hampshire's tax law did not violate the Commerce Clause of the U.S. Constitution, as it was a compensatory tax designed to make interstate commerce bear a burden already borne by intrastate commerce. The justice disagreed with majority’s view that this case is similar to those where states attempted to protect their local industries from out-of-state competition through discriminatory taxation, arguing instead that New Hampshire's tax aimed at equalizing treatment between residents and non-residents rather than discriminating against interstate commerce. Furthermore, they contended that if every state adopted similar laws there would be no multiple or duplicative taxation on interstate income which could impede free trade among states.