In the case of Gelbard et al. v. United States (1971), the U.S. Supreme Court ruled in favor of two witnesses who refused to testify before a grand jury, citing that their testimony was derived from illegal wiretaps which violated their Fifth Amendment rights against self-incrimination. The government argued that they could not invoke this privilege as they were not at risk of being prosecuted based on these wiretaps and thus, held them in contempt for refusing to answer questions before the grand jury. However, the court disagreed with this argument stating that Title III of Omnibus Crime Control and Safe Streets Act 1968 protected individuals from being questioned based on evidence obtained through unlawful surveillance methods even if it's used only for questioning rather than prosecution purposes.

In the dissenting opinion for Gelbard et al. v. United States, Justice Harlan argued that the majority's decision to allow defendants in a criminal case to challenge their indictment based on illegal wiretaps was misguided and could lead to unnecessary delays in court proceedings. He contended that such challenges should be reserved for after conviction, as is standard with other types of constitutional violations alleged by defendants. Furthermore, he disagreed with the majority's interpretation of Title III of the Omnibus Crime Control and Safe Streets Act; he believed it did not provide any basis for pretrial motions related to electronic surveillance evidence used before grand juries. In his view, this law only provided remedies against those who actually conducted or authorized unlawful interceptions - not against prosecutors who later made use thereof before a grand jury.