In the United States v. Janis case of 1975, the U.S. Supreme Court ruled that evidence illegally seized by state law enforcement officers could be used in federal civil proceedings. The case involved Mark Janis, who was under investigation for illegal gambling operations. Local police obtained a search warrant and confiscated $4,940 from his home but this seizure was later deemed unconstitutional due to lack of probable cause for the warrant issuance. Despite this ruling, the Internal Revenue Service (IRS) sought to use this money as evidence in a tax evasion lawsuit against Janis on grounds that it represented unreported income from his alleged illegal activities. The court held that while such evidence would not be admissible in criminal trials due to Fourth Amendment protections against unreasonable searches and seizures - known as "exclusionary rule" - these protections did not extend to federal civil cases like those pursued by IRS because potential benefits of deterring unlawful police conduct were outweighed by societal costs incurred if civil proceedings were hampered.

In the dissenting opinion for United States et al. v. Janis, 1975, Justice Brennan argued that the majority's decision to allow illegally seized evidence in a civil proceeding was inconsistent with previous rulings and undermined Fourth Amendment protections against unreasonable searches and seizures. He contended that allowing such evidence would incentivize law enforcement officers to conduct illegal searches because they could still use any discovered evidence in subsequent civil proceedings even if it were excluded from criminal trials due to its unlawful acquisition. Furthermore, he believed this ruling blurred the distinction between criminal and civil proceedings by treating them as interchangeable arenas for punishment rather than separate systems with distinct purposes and standards of proof. Lastly, he expressed concern about potential abuse of power by government officials who might exploit this loophole to harass or intimidate citizens without fear of legal repercussions.