A search at an international boundary of a person, a vehicle, or goods entering the United States may be carried out without a search warrant and in the absence of probable cause or even suspicion. In United States v. Ramsey (1977) the Supreme Court said that this extraordinary power, which also allows the government to open international mail entering the United States, "is grounded in the recognized right of the sovereign to control … who and what may enter the country." The First Congress, in 1789, authorized warrantless searches of vessels suspected of carrying goods on which customs duty had been evaded, and similar provisions have been enacted subsequently. As the Court held in almeida-sanchez v. united states (1973), such a search may be conducted not only at the border itself but also at its "functional equivalent," such as "an established station near the border," or "a point marking the confluence of two or more roads that extend from the border," or an airplane arriving on a nonstop flight from abroad.
Under United States v. Brignoni-Ponce (1975) an automobile may not be stopped by a roving patrol car miles from the border (in an area that is not its legal equivalent) to determine whether the occupants are illegal aliens unless there is reasonable suspicion. Under United States v. Martinez-Fuerte (1976) automobiles may be stopped for this purpose at fixed checkpoints; in these circumstances the opportunity of officers to act arbitrarily is limited.
Jacob W. Landynski
"Border Search." Encyclopedia of the American Constitution. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/politics/encyclopedias-almanacs-transcripts-and-maps/border-search
"Border Search." Encyclopedia of the American Constitution. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/politics/encyclopedias-almanacs-transcripts-and-maps/border-search