To refrain from answering questions by law enforcement when there’s no warrant, or you don’t know why you’re being asked, is generally thought to be acting within your Fourth Amendment rights.
On the Texas border, it gets sticky. U.S. Citizens have recently been punished for exercising the right to not answer questions. A graduate student was home visiting Brownsville when he got stopped at the airport and got approached by agents. He was asked questions, but declined to answer.
“Figueredo was charged with three misdemeanors: failure to identify, which under Texas law applies only when a person being lawfully arrested refuses to give a peace officer his or her name, birth date or address; resisting arrest; and obstructing a passageway. Morales also was charged with obstructing a passageway and interfering with public duty….
“Many believe the checkpoints violate the Fourth Amendment prohibition on unreasonable searches and seizures. In any case, you generally don’t have to answer Border Patrol agents when you’re at these internal checkpoints. If an agent has probable cause to think you’re in the country illegally—and refusing to answer their questions isn’t probable cause—the agent can briefly detain you. A fascinating case in Brownsville has put this issue to the test.” –Texas Observer
I wonder what they consider “probable cause” to be. It’s a case of petty details being exploited by law enforcement, making life very difficult for American citizens visiting their hometown of Brownsville. Imagine going home to visit, being asked questions by inquiring government agents, then getting arrested, then being charged on a bunch of counts…then having to hire a lawyer, having it take a year or more out of your life…all because a few border patrol agents blew some petty details out of proportion as they acted erroneously.