"The Fourth Amendment to the Constitution contains a border-related exception to unreasonable search and seizure laws, permitting searches at border checkpoints that wouldn't be permitted elsewhere. But federal statute 8 CFR 287.1 (a)(1-3) defines the border zone for enforcement purposes as encompassing an area within 100 miles of the actual border, with the possibility of extending it further under certain circumstances. This means that the US Border Patrol could conceivably set up random checkpoints asking travelers for a passport in places like Columbus, Ohio; Houston; or anywhere in the state of Florida. And, in fact, it appears that it has been doing exactly this."

http://arstechnica.com/security/news/2008/10/aclu-23-of-us-p...