A more thorough explanation:

Immigration & Naturalization Service v. Delgado was a case heard by the Supreme Court in 1984. The case was about whether the Immigration and Naturalization Service (INS) violated the Fourth Amendment by conducting factory surveys and questioning workers about their citizenship. The Fourth Amendment protects individuals from unreasonable seizures and detention by the police.

The INS agents walked through factories and questioned workers about their citizenship in an attempt to find undocumented noncitizens. If the employee responded to the INS agents by saying that he was a U.S. citizen, the agents would move on to another employee. However, if the factory worker gave an unsatisfactory reply or admitted to being an alien, the INS agent asked for the employee’s immigration papers.

The Supreme Court held that the factory surveys conducted by the INS did not constitute a seizure of the entire work force under the Fourth Amendment. The Court explained that an unreasonable seizure occurs when, considering all the surrounding circumstances of the detention, a reasonable person believes he does not have the freedom to leave during the questioning. During the surveys, several INS agents stationed themselves near the factory building’s exits. The Court rejected the claim that the placement of INS agents at the exits of the factories constrained the employees’ freedom to leave. The Court concluded that a seizure of the entire work forces did not occur. Consequently, it found no violation of the Fourth Amendment.

The Court also held that the interrogation of the individual respondents did not constitute a seizure under the Fourth Amendment. The Court applied the reasonable person test. Although the employees argued that they suffered psychologically from the questioning, the Court did not find that they reasonably feared being arrested and found that they reasonably did not feel constrained. The Court asserted that the INS did not constrain their physical movement. The Court further supported its decision by noting the brevity of the questioning of the individual workers.

Example: The INS conducted factory surveys and questioned workers about their citizenship to find undocumented noncitizens. The Supreme Court held that the factory surveys and individual questioning did not violate the Fourth Amendment because the INS did not unreasonably seize or detain the workers.