In the case of Hawkins v. United States (1958), the U.S Supreme Court ruled that a wife's voluntary testimony about her husband's illegal activities was admissible in court, even if they were still married at the time of his alleged crimes. The couple had divorced by the time she testified against him. This decision overturned an earlier ruling which stated that confidential communications between spouses during their marriage are privileged and cannot be used as evidence in criminal proceedings after divorce or separation. The court held that this privilege did not apply when one spouse is willing to testify against another, thereby allowing Mrs. Hawkins' testimony to stand as evidence in Mr.Hawkins' trial for conspiracy to violate federal liquor laws.

In the dissenting opinion for Hawkins v. United States, Justice Brennan disagreed with the majority's interpretation of a statute regarding conspiracy to commit an offense against the U.S. He argued that it was not enough for two people to agree on committing an illegal act; they must also take some action towards carrying out their plan. In this case, he believed that there was insufficient evidence of such action by Mr. and Mrs. Hawkins beyond mere agreement or intent to defraud revenue laws through false tax returns preparation business scheme. Justice Brennan further contended that Congress intended "overt act" requirement in every federal conspiracy prosecution unless expressly provided otherwise in law - a view contrary to majority’s interpretation which exempted certain conspiracies from this requirement based on historical context and statutory language analysis. He warned about potential misuse of power by prosecutors who could charge individuals with conspiracy without needing substantial proof of any real steps taken towards executing their alleged plans – thus infringing upon individual liberties protected under due process clause.