In Liparota v. United States (1984), the Supreme Court ruled that in order to convict someone of illegally acquiring food stamps, it must be proven they knew their actions were unlawful. The case involved a man named Peter Liparota who was charged with unlawfully acquiring and possessing food stamps, which is a violation of federal law. He argued that he didn't know his actions were illegal and therefore couldn't be convicted under this statute. The government contended that ignorance of the law wasn't an acceptable defense, but the Supreme Court disagreed with this argument in a 5-4 decision favoring Liparota. They held that for such conviction to occur, there must be proof beyond reasonable doubt about defendant's knowledge regarding illegality of his conduct.

The dissenting opinion in Liparota v. United States argued that the majority's interpretation of the statute at issue was too narrow and failed to consider its broader purpose: preventing fraud against a federal program. The dissenters believed that it should not be necessary for prosecutors to prove specific intent to defraud, as this would make it more difficult to convict those who knowingly misuse food stamps but claim ignorance of the law. They pointed out that other statutes with similar language had been interpreted without requiring proof of knowledge about illegality, and suggested that Congress intended a broad reading when they enacted this legislation. Therefore, they disagreed with the majority's decision overturning Liparota’s conviction based on lack of evidence proving his awareness about violating laws related to food stamp usage.