In the United States v. Mendenhall case of 1979, the Supreme Court ruled that a person is "seized" within the meaning of Fourth Amendment only when, by means of physical force or show of authority, his freedom of movement is restrained and in light of all circumstances surrounding incident, a reasonable person would believe he was not free to leave. The court held that respondent had not been seized when she was approached by DEA agents at airport since they did not draw their guns or otherwise intimidate her into responding to their questions and going with them to office for search; thus there was no violation on part from law enforcement officers. Furthermore, it determined that consent given under such non-coercive conditions could be considered voluntary hence making subsequent discovery admissible evidence against her.

In the dissenting opinion for United States v. Mendenhall, Justice Marshall argued that Ms. Mendenhall was indeed seized when stopped by DEA agents in the airport and thus her Fourth Amendment rights were violated. He contended that a reasonable person would not have felt free to leave under such circumstances given the show of authority by federal law enforcement officers. Furthermore, he disagreed with the majority's view on consent, arguing that it cannot be truly voluntary if it is obtained after an illegal seizure has occurred; hence any evidence procured as a result should be excluded from trial proceedings due to its tainted nature (fruit of poisonous tree doctrine). Additionally, he criticized their reliance on factors like race or previous criminal record in determining suspicious behavior which could lead to racial profiling and other forms of discrimination.