In the McKee v. United States case of 1896, the U.S Supreme Court ruled on a matter concerning customs duties. The plaintiff, McKee, was an importer who had paid duties under protest on imported goods and sought to recover them from the government. He argued that he should have been charged less due to a clause in tariff legislation which stated that if any country imposed "unjust" or "unreasonable" import charges on American products then similar rates could be applied by America in return. However, this argument was rejected by both lower courts and eventually by the Supreme Court as well. The court held that it did not possess jurisdiction over political matters such as determining what constituted unjust or unreasonable tariffs; these were issues for Congress and the President to decide upon. Furthermore, they found no evidence of any official proclamation stating that higher rates were being imposed because of unfair foreign practices - thus there was no legal basis for charging reduced fees. This decision reinforced separation of powers principles within US governance structure while also clarifying how trade laws are interpreted and enforced.

In the dissenting opinion for McKee v. United States, Justice Harlan argued that the majority's decision was a misinterpretation of the Sherman Anti-Trust Act and its intent to protect competition. He believed that this case did not involve interstate commerce but rather local trade within a single state, thus falling outside federal jurisdiction. Furthermore, he contended that even if it were considered interstate commerce, it would still be exempt from antitrust laws as sugar refining is not inherently monopolistic or anti-competitive in nature; instead, any monopoly status achieved by McKee was due to superior business acumen and efficiency rather than unfair practices. Therefore, according to Justice Harlan's interpretation of the law and facts at hand, no violation had occurred warranting government intervention under the Sherman Act.