In Mancusi v. DeForte 1967, the U.S. Supreme Court ruled on a case involving Fourth Amendment rights in relation to union offices. The respondent, Anthony DeForte, was an official of a labor union who had been summoned by a grand jury investigating alleged criminal activities within his organization. He refused to answer questions based on self-incrimination grounds and subsequently had his office searched without warrant by FBI agents who seized several documents as evidence against him for obstruction of justice charges. DeForte argued that this violated his Fourth Amendment rights against unreasonable searches and seizures since he personally used the office space regularly even though it wasn't exclusively assigned to him. The court held that despite not having exclusive use or possession of the premises, DeForte still had legitimate expectation of privacy in the office which made it subject to Fourth Amendment protections. However, they also found that under certain circumstances where there is probable cause and exigent circumstances exist (such as risk of immediate destruction or removal), warrantless search could be justified - but such conditions were not present in this case hence making seizure unlawful.

In the dissenting opinion for Mancusi v. DeForte, Justice White argued that the Fourth Amendment rights of union members do not extend to their offices because they lack a reasonable expectation of privacy in such spaces. He contended that DeForte's office was not his personal property but belonged to the union and was accessible by other employees, thus negating any claim to privacy. Furthermore, he stated that even if there were an invasion of privacy, it would be justified due to compelling government interest in investigating potential corruption within labor unions. The majority's decision could potentially hinder future investigations into similar matters by requiring warrants where they may not have been necessary before.