The Harding v. Illinois case in 1904 revolved around a dispute over the legality of an Illinois law that prohibited non-residents from fishing with seines (a type of fishing net) in state waters, while allowing residents to do so. The plaintiff, Mr. Harding, was a resident of Kentucky who argued that this law violated his privileges and immunities as a U.S citizen under Article IV Section 2 Clause 1 of the Constitution which prohibits states from discriminating against citizens from other states. However, the Supreme Court ruled against him stating that the Privileges and Immunities Clause did not guarantee protection for all rights but only fundamental ones related to national citizenship such as access to courts or interstate travel. It held that commercial activities like seine fishing were subject to regulation by individual states based on their own policies and interests. Therefore, it concluded that Illinois' restriction on non-resident seine fishing was constitutional since it served legitimate conservation purposes without infringing upon any fundamental rights protected by the Privileges and Immunities clause.

The dissenting opinion in the case of Harding v. Illinois argued that the majority's decision to uphold a state law prohibiting non-residents from fishing in its waters was inconsistent with previous rulings and violated principles of equal protection under the Constitution. The dissent pointed out that while states have broad powers to regulate their natural resources, these regulations should not discriminate against citizens of other states without substantial justification. They contended that this ruling contradicted earlier decisions which held that privileges and immunities clause protected citizens' rights to earn a living across state lines, including through commercial fishing activities. Furthermore, they disagreed with the majority's assertion about conservation being an adequate reason for such discrimination as there were no factual findings showing overfishing or resource depletion by non-residents specifically.