In the 1965 case Castaldi v. United States, the Supreme Court ruled on an appeal by Joseph Castaldi who had been convicted of tax evasion. The main issue was whether or not a document used as evidence against him should have been admitted in court since it was obtained without a warrant and thus potentially violated his Fourth Amendment rights to protection from unreasonable searches and seizures. However, the Supreme Court upheld his conviction with a 7-2 decision, ruling that there were no constitutional violations because he voluntarily gave up possession of this document when he handed it over to his accountant for tax preparation purposes. Therefore, its seizure did not constitute an illegal search or seizure under the Fourth Amendment.

In the dissenting opinion for Castaldi v. United States, Justice Douglas argued that the majority's decision to uphold Castaldi's conviction was a violation of his Fifth Amendment rights against self-incrimination. He contended that by allowing evidence obtained through wiretapping without consent or warrant, it effectively forced individuals to testify against themselves in court. Furthermore, he criticized the majority’s reliance on Lopez v. United States as precedent because it involved consensual recording rather than non-consensual wiretapping and thus did not apply directly to this case. In addition, Justice Douglas expressed concern about potential abuses of power if law enforcement agencies were allowed unrestricted use of such surveillance methods without judicial oversight or individual consent.