In the United States v. Dudley case of 1898, the Supreme Court ruled on a matter involving customs duties. The defendant, Dudley, imported iron ore into the U.S and argued that it should be classified under "iron ore" for duty purposes which had no import tax according to tariff laws at that time. However, the government contended that it was pig iron - not in pigs - and thus subject to a duty of $0.75 per ton as per paragraph 123 of Tariff Act of July 24th, 1897. The court held in favor of Dudley stating that while there is ambiguity about what constitutes 'pig iron', Congress intended to impose duties only on manufactured articles rather than raw materials such as ores from which they are made; hence his imports were exempted from any custom duties.

In the dissenting opinion for United States v. Dudley, it was argued that the court's decision to uphold Dudley's conviction on charges of conspiracy and fraud undermined the principle of due process. The dissenting justices believed that there were significant issues with how evidence had been collected and presented during trial, which they felt compromised its reliability. They also took issue with how certain legal standards had been applied in this case, arguing that these applications were inconsistent with established precedent. Furthermore, they expressed concern over what they saw as an overly broad interpretation of conspiracy law by the majority opinion - one which could potentially criminalize a wide range of otherwise lawful activities if left unchecked. Ultimately, their disagreement centered around questions about fairness in both procedure and substance; while acknowledging the importance of combating fraud and protecting public interests, they maintained that such efforts should not come at expense of individual rights or legal integrity.