As part of its immigration enforcement efforts, CBP boards buses and trains in the 100-mile border region either at the station or while the bus is on its journey. More than one officer usually boards the bus, and they will ask passengers questions about their immigration status, ask passengers to show them immigration documents, or both. These questions should be brief and related to verifying one’s lawful presence in the U.S. Although these situations are scary, and it may seem that CBP agents are giving you an order when they ask you questions, you are not required to answer and can simply say you do not wish to do so. As always, you have the right to remain silent.
Refusing to answer CBP’s questions may result in the agent persisting with questioning. If this occurs, you should ask if you are being detained. Another way to ask this is to say, “am I free to leave?” If the agent wishes to actually detain you — in other words, you are not free to leave — the agent needs at least reasonable suspicion that you committed an immigration violation to do so. Also, if an agent begins to question you about non-immigration matters, say to ask about drug smuggling, or if they haul you off the bus, they need at least reasonable suspicion that you committed an offense in order to briefly detain you while they investigate. You can ask an agent for their basis for detaining you, and they should tell you.
The longer CBP detains you the more suspicion they need — eventually they will need probable cause once the detention goes from brief to prolonged. If the agent arrests you or searches the interior of your belongings, they need probable cause that you committed an offense. You can ask the agent to tell you their basis for probable cause, and they should be able to articulate their suspicion.