Illustration by Steve Breen for inewsource.

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The following overview is provided for general informational purposes only. It is not legal advice, nor is it intended to be. The reporter is not an attorney, and the information could change as laws or policies are updated. Readers should consult with an attorney before taking any action related to the issues discussed below.

Whether we notice it or not, residents of San Diego and Imperial counties are among the 200 million U.S. residents who live within the federal immigration enforcement zone – a territory stretching 100 miles inward from every land and maritime border.

In that zone, U.S. Customs and Border Protection – the largest law enforcement agency in the country – can operate immigration checkpoints, board buses and trains and perform “roving patrols” on roads and highways in search of people committing immigration offenses or other federal crimes. 

But CBP’s powers here aren’t limitless. People in the United States, regardless of immigration status, are protected by the Fourth Amendment from arbitrary searches and seizures.

Click on each drop down to learn more about specific situations. 

When federal agents can stop, search and question

Federal agents, just like local law enforcement officers, must meet certain legal thresholds in order to carry out certain activities in the furtherance of their mission. For Border Patrol, that mission is to apprehend violators of federal immigration law. 

Federal agents need reasonable suspicion to: 

  • Pull a driver over 
  • Detain someone. If they ask if they are free to leave and the agent says no, they are being detained.

And they need probable cause to: 

  • Make an arrest.
  • Search someone’s vehicle or belongings (unless they are given permission).

According to the Supreme Court, an officer has reasonable suspicion if they can “point to specific and articulable facts which, taken together with rational inferences . . . reasonably warrant” a person’s detention. In the context of immigration law, agents need reasonable suspicion that a civil or criminal immigration violation has occurred.

And probable cause is defined as when “the facts and circumstances within the officers’ knowledge … are sufficient in themselves to warrant a belief by a man of reasonable caution that a crime is being committed.”

In general, federal immigration agents can only enforce federal immigration law, so they can’t get a driver in trouble for speeding, for example. 

However, agents can use that a driver was speeding as part of their basis for reasonable suspicion or probable cause. 

In some parts of the country, agents can rely in part on a person’s race and ethnicity in determining that basis, but those factors cannot be the sole basis for reasonable suspicion or probable cause. Civilians can always choose to remain silent or decline to answer questions without a lawyer.


There are as many as 13 checkpoints, temporary or permanent, operating in Southern California, including on the heavily traveled westbound Interstate 8 in Pine Valley, northbound Interstate 5 in San Clemente, and northbound Interstate 15 near Temecula, and along more rural routes near Campo, Ocotillo and the Salton Sea. 

When passing through a checkpoint, Border Patrol can ask the driver and passengers a few questions related to their immigration status and can visually inspect the outside of the vehicle. 

Agents may also use drug-sniffing dogs around stopped vehicles or send vehicles to a secondary inspection area for further, but brief, questioning and visual inspection. 

They still need reasonable suspicion to question drivers longer or detain drivers. Agents cannot arrest drivers or physically inspect vehicles or belongings without probable cause. 

It’s a felony to flee an immigration checkpoint. 

‘Roving Patrols’

When Border Patrol agents conduct “roving patrols,” during which agents drive throughout the enforcement zone looking for immigration or other federal violations, they need to have reasonable suspicion of criminal activity to pull over a vehicle and probable cause to search the vehicle. 

It is illegal for agents to pull over vehicles based solely on the race or ethnicity of the driver or occupants, but in practice, it happens, according to the ACLU.

Buses and Trains

Border Patrol can board buses and trains within the enforcement zone to question passengers about immigration status, travel plans and luggage. Passengers can refuse to comply or answer questions, but doing so could lead to prolonged questioning. 

United States citizens are not required to carry proof of their citizenship with them at all times. Others over the age of 18 with legal immigration documents are required to carry them at all times. 

If an agent is questioning a passenger and they do not feel free to leave, the agent needs reasonable suspicion to detain them. At some point, when the detention goes from brief to prolonged and becomes an arrest, the agent needs probable cause.

Want to know more? Check out the American Civil Liberties Union’s “Know Your Rights” guide to Border Patrol’s 100-mile enforcement zone. 

Explore more stories from our investigation into Border Patrol’s vehicle pursuit policies.

Type of Content

News: Based on facts, either observed and verified directly by the reporter, or reported and verified from knowledgeable sources.

Sofía Mejías-Pascoe is a border and immigration reporter covering the U.S.-Mexico region and the people who live, work and pass through the area. Mejías-Pascoe was previously a general assignment reporter and intern with inewsource, where she covered the pandemic’s toll inside prisons and detention...