In the United States v. Brignoni-Ponce case of 1974, the Supreme Court ruled that random stops and interrogations about citizenship status by roving patrols without reasonable suspicion were a violation of the Fourth Amendment, which protects against unreasonable searches and seizures. The case arose when a vehicle was stopped near the Mexican border solely because its occupants appeared to be of Mexican descent. During this stop, one occupant admitted to being an illegal alien leading to his arrest. However, it was determined that racial appearance alone did not provide sufficient grounds for reasonable suspicion necessary for such stops under law enforcement authority granted by Immigration and Nationality Act (INA). Therefore, while immigration officers could consider apparent Mexican ancestry as one factor in deciding whether there is reasonable suspicion warranting a stop near borders or their functional equivalents; they cannot use it as sole reason.

In the dissenting opinion for United States v. Brignoni-Ponce, Justice William Rehnquist argued that the majority's decision to require reasonable suspicion for roving patrols near the border would significantly hinder law enforcement efforts to control illegal immigration. He contended that this ruling was inconsistent with previous decisions allowing searches and seizures without probable cause in other contexts such as airport security checks and border crossings. Furthermore, he believed it was impractical to expect officers patrolling vast stretches of remote areas along the U.S.-Mexico border to have specific reasons for suspecting each individual vehicle they stop. Instead, he suggested a more flexible approach where factors like proximity to the border or suspicious behavior could justify stops without requiring concrete evidence of criminal activity.