Is a vehicle stop at a permanent immigration checkpoint an "seizure" for Fourth Amendment purposes?

The Fourth Amendment requires that searches and seizures be reasonable. See U.S. CONST. amend. IV. Generally, a search or seizure is unreasonable in the absence of individualized suspicion of wrongdoing. Id. While a vehicle stop at an immigration checkpoint is a "seizure," Border Patrol may stop or slow vehicles, and question occupants at a checkpoint for Fourth Amendment purposes. See United States v. Martinez-Fuente, 428 U.S. 543, 562 (1976). Permanent interior checkpoints, such as the Highway 86 checkpoint, are maintained at or near important roads leading away from the border and "operate on a coordinated basis designed to avoid circumvention by smugglers and others who transport the illegal aliens." Id. at 552. A vehicle may be stopped at a permanent immigration checkpoint for brief initial questioning, and then referred to a secondary inspection area for further questioning "in the absence of an individualized suspicion." Id. at 562. An officer has wide discretion in making referrals to secondary. See id. at 564.