The U.S. Supreme Court case Immigration and Naturalization Service v. Lopez-Mendoza et al., 1983, dealt with the issue of whether evidence obtained through illegal arrests could be used in deportation proceedings. The defendants were two undocumented immigrants who had been arrested without a warrant or probable cause by INS officers, which they argued violated their Fourth Amendment rights against unreasonable searches and seizures. In a 5-4 decision, the court ruled that the exclusionary rule (which generally prohibits illegally obtained evidence from being used in criminal trials) did not apply to civil proceedings such as deportations because these are not intended to punish past transgressions but rather prevent ongoing violations of law. Therefore, even though their arrests may have been unlawful, the evidence gathered could still be used for deportation purposes.

In the dissenting opinion for Immigration and Naturalization Service v. Lopez-Mendoza, Justice Brennan argued that the majority's decision to allow evidence obtained through illegal arrests in deportation proceedings was a departure from established Fourth Amendment principles. He contended that this ruling undermined the fundamental rights of individuals against unreasonable searches and seizures by law enforcement officials. Furthermore, he expressed concern about potential abuses of power by immigration officers due to their broad authority under immigration laws. He also disagreed with the majority's view that excluding illegally obtained evidence would not deter unlawful conduct by immigration officers because they are primarily concerned with deportations rather than criminal prosecutions. Instead, he believed such exclusion would indeed serve as an effective deterrent against constitutional violations.