In the case of United States v. Biswell, the Supreme Court ruled in favor of upholding a warrantless search under the Gun Control Act of 1968. The defendant, Raymond Biswell, was a licensed firearms dealer who sold a prohibited weapon to an undercover agent without proper documentation. After this sale took place, law enforcement officials conducted an unannounced inspection and found additional illegal weapons on his premises. Biswell argued that these searches violated his Fourth Amendment rights against unreasonable searches and seizures because they were conducted without a warrant or probable cause. The court disagreed with this argument stating that when someone enters into regulated business activities such as selling firearms; there is reduced expectation of privacy due to regular inspections required by law for public safety reasons. Furthermore, it was noted that if every inspection had to be preceded by obtaining warrants would frustrate federal regulatory scheme designed to prevent trafficking in dangerous weapons.

In the dissenting opinion for United States v. Biswell, Justice Thurgood Marshall argued that the majority's decision expanded police power in a way that threatened Fourth Amendment protections against unreasonable searches and seizures. He disagreed with their interpretation of "reasonable expectation of privacy," asserting that even regulated businesses should not be subject to warrantless inspections without explicit consent or legislative provision for such inspections. Furthermore, he contended that just because an industry is pervasively regulated does not mean its participants surrender all expectations of privacy within it. He also expressed concern about potential abuses by law enforcement under this ruling, as they could use regulatory inspection as a pretext to conduct criminal investigations without obtaining necessary warrants first.