Is a stop at a permanent immigration checkpoint constitute a seizure under the Fourth Amendment?

A stop at a permanent immigration checkpoint constitutes a "seizure" within the meaning of the Fourth Amendment. United States v. Martinez-Fuerte, 428 U.S. 543, 556, 96 S.Ct. 3074, 3082, 49 L.Ed.2d 1116 (1976). Such a stop is constitutional so long as the scope of the detention is limited to a few brief questions about immigration, the production of immigration documents, and a "visual inspection of the vehicle ... limited to what can be seen without a search." Id. at 558, 96 S.Ct. at 3083. The government may refer any vehicle to a secondary area for further immigration questioning "in the absence of any individualized suspicion...." Id. at 562, 96 S.Ct. at 3805.