In the case of United States v. First National City Bank, 1964, the U.S Supreme Court ruled in favor of the government and against First National City Bank (now Citibank). The bank had refused to provide information about one of its customers' accounts to a grand jury investigating tax evasion on grounds that it would violate New York state law protecting banking secrecy. However, the court held that federal law took precedence over state laws in this matter. Therefore, banks could not refuse subpoenas for customer records from federal authorities based on conflicting state privacy laws. This decision clarified that under national supremacy principles outlined by Article VI of Constitution, when there is a conflict between federal and state law regarding disclosure requirements for financial institutions involved in criminal investigations or proceedings at a federal level; Federal Law prevails.

In the dissenting opinion for United States v. First National City Bank, it was argued that the majority had misinterpreted and overstepped their authority under the Trading with The Enemy Act. The dissenting justices believed that this act did not give the President or his delegates unlimited power to freeze assets indefinitely without any form of judicial review or due process. They also disagreed with how broadly "enemy" was defined in this case, as they felt it could potentially include innocent parties who were merely caught up in a foreign conflict through no fault of their own. Furthermore, they expressed concern about potential abuses of power if such broad interpretations were allowed to stand unchallenged.