In the United States v. Hemmer case of 1915, the Supreme Court ruled on a matter concerning customs duties. The defendant, John Hemmer, was charged with smuggling goods into the country without paying appropriate import taxes. He argued that he had not been properly informed about his rights and obligations under customs law at the time of entry into U.S territory. However, this argument was rejected by both lower courts and eventually by the Supreme Court as well. The court held that ignorance or misunderstanding of laws does not exempt individuals from their obligation to comply with them; it is presumed that everyone knows what these laws are once they have been enacted and published for public knowledge. Therefore, any failure to pay required duties due to lack of awareness or understanding would still be considered illegal activity punishable under federal law. This decision reinforced an important principle in American jurisprudence: "ignorance of law excuses no one". It also underscored government's right to enforce its tax regulations strictly in order to protect domestic industries and generate revenue for public services.

In the dissenting opinion for United States v. Hemmer, it was argued that the defendant's conviction should not have been upheld because there were significant issues with how evidence was obtained and presented in court. The justice believed that Hemmer’s Fourth Amendment rights had been violated due to an unlawful search and seizure of his property by law enforcement officers who did not possess a valid warrant at the time of their investigation. Furthermore, they contended that this illegally seized evidence should have been excluded from trial proceedings as per the exclusionary rule which prohibits such use of unlawfully obtained evidence in criminal trials. They also expressed concerns about potential violations of Hemmer's Fifth Amendment rights against self-incrimination during police interrogations without proper legal counsel present or informed consent given by him regarding these constitutional protections he possessed under U.S law.