It is a simple question that Carlota Wray has come to regard as an insult: "Are you a US citizen?"

For the record, the answer is yes: Wray has lived in the US for more than 30 years, is married to an American and became a naturalised citizen about a decade ago. But she resents being quizzed about her immigration status, and is sometimes asked to prove it, when she leaves her home in the tiny Arizona border town of Arivaca for routine trips to neighbouring places a couple of times a week.

So do a number of other Arivaca residents. They have stepped up protests against a Border Patrol road checkpoint just outside the town, complaining that it is ineffective, a nuisance, an invasion of civil rights and an invitation for agents to conduct racial profiling.