The Fourth Amendment of the U.S. Constitution protects Americans from random and arbitrary stops and searches.
According to the government, however, these basic constitutional principles do not apply fully at our borders. For example, at border crossings (also called "ports of entry"), federal authorities do not need a warrant or even suspicion of wrongdoing to justify conducting what courts have called a "routine search," such as searching luggage or a vehicle.
Even in places far removed from the border, deep into the interior of the country, immigration officials enjoy broad—though not limitless—powers. Specifically, federal regulations give U.S. Customs and Border Protection (CBP) authority to operate within 100 miles of any U.S. "external boundary."
In this 100-mile zone, Border Patrol agents have certain additional authorities. For instance, Border Patrol can operate immigration checkpoints.
Border Patrol, nevertheless, cannot pull anyone over without "reasonable suspicion" of an immigration violation or crime (reasonable suspicion is more than just a "hunch"). Similarly, Border Patrol cannot search vehicles in the 100-mile zone without a warrant or "probable cause" (a reasonable belief, based on the circumstances, that an immigration violation or crime has likely occurred).
In practice, Border Patrol agents routinely ignore or misunderstand the limits of their legal authority in the course of individual stops, resulting in violations of the constitutional rights of innocent people. These problems are compounded by inadequate training for Border Patrol agents, a lack of oversight by CBP and the U.S. Department of Homeland Security, and the consistent failure of CBP to hold agents accountable for abuse. No matter what CBP officers and Border Patrol agents think, our Constitution applies throughout the United States, including within this “100-mile border zone.”