In the 1985 case United States v. Koecher, Karl F. Koecher and his wife Hana were charged with espionage for allegedly spying on behalf of Czechoslovakia while working as translators at the United Nations and other U.S agencies. The couple was arrested in November 1984 after a lengthy FBI investigation revealed they had been passing classified information to foreign agents since 1973. In an unprecedented move, the Supreme Court allowed closed-door proceedings due to national security concerns, marking one of few times that such secrecy has been permitted in American courts. The government argued that public disclosure could compromise intelligence sources and methods used during investigations into espionage activities by Eastern Bloc countries during the Cold War era.

In the dissenting opinion for United States v. Koecher, Justice Brennan argued that the majority's decision to allow evidence obtained through a warrantless wiretap under the Foreign Intelligence Surveillance Act (FISA) was unconstitutional. He contended that FISA violated Fourth Amendment protections against unreasonable searches and seizures by allowing surveillance without probable cause of criminal activity. Furthermore, he criticized the majority for not addressing whether or not FISA met constitutional standards for warrants in general - specifically its lack of requirement to notify subjects of surveillance after it has ended. Brennan also expressed concern about potential abuse of power, stating that this ruling could lead to unchecked government intrusion into private lives under the guise of foreign intelligence gathering.