Acting on lawfully-obtained warrants, the Immigration and Nationalization Service (INS) (defendant) conducted two searches of a garment factory called Southern California Davis Pleating Company (Davis Pleating), in search of illegal aliens. A separate search was conducted at Mr. Pleat, another garment factory. During the searches, INS agents positioned themselves near exits and conducted a thorough sweep of the building, questioning factory employees regarding their citizenship status. While the INS questioned employees at their work stations, other employees continued with their work and were allowed to freely walk around within the factory. Delgado and three other employees as well as their union representative (collectively Plaintiffs) filed suit against the INS in federal district court and claimed that the searches violated their Fourth Amendment rights and requested declaratory relief. The district court dismissed the union from the suit for lack of standing and held for the INS. The court concluded that none of the Plaintiffs had been detained under the Fourth Amendment during the searches and therefore no unconstitutional activity took place. Plaintiffs appealed. The court of appeals reversed and held that the entire workforce had been seized for the duration of each INS search because agents had been stationed near building exits, leading a reasonable worker to believe that he or she was not free to leave. The U.S. Supreme Court granted certiorari to review.