In the case of United States v. Cardiff, the Supreme Court ruled in favor of defendant Robert E. Cardiff who was charged with violating a federal statute requiring him to register as an employer under the Social Security Act. The court held that because it is not clear from reading this law whether or not Mr. Cardiff should have registered, he could not be convicted for failing to do so. The key issue revolved around ambiguity in legal language and its interpretation by individuals subject to those laws; specifically, whether ignorance or misunderstanding due to ambiguous wording can serve as a valid defense against charges of non-compliance. The ruling emphasized that no one may be required at peril of life, liberty or property to speculate as to the meaning of penal statutes and that all are entitled to be informed about what these statutes command or forbid.

In the dissenting opinion for United States v. Cardiff, Justice Douglas argued that the majority's interpretation of a statute requiring mine operators to submit accident reports was too broad and vague. He contended that it was unreasonable to expect mine operators to understand which accidents they were required to report without clear guidelines from Congress or regulatory agencies. Furthermore, he suggested that this ambiguity could lead to arbitrary enforcement by government officials who might interpret the law differently in different circumstances. In his view, such vagueness violated due process rights because individuals should have fair notice of what conduct is prohibited by law before being penalized for violating it.