If any U.S. citizen knows his legal rights, Hassan Shibly does. A law student at the University of Buffalo in New York, he has also clerked for a judge at New York's State Supreme Court.
Last summer he took his wife and son on a pilgrimage to the Muslim holy city of Mecca in Saudi Arabia, and to visit to his family in Syria. Upon return, he says, he was taken aside for questioning at New York's John F. Kennedy airport.
Shibly says an agent asked him how many gods and prophets he believes in and whether he studies his religion full time.
"And I think one of the most offensive things was in the end," Shibly recalled, "when he was trying to wrap things up, he said: 'I hope you're not annoyed. It's just that we want to protect this country from bombs and terrorism.'"
Lawrence Ho is also a U.S. citizen, and a Muslim convert. He was stopped at a border crossing with Canada.
Ho says he was held for four hours and asked religious questions interrogation-style - in a closed room, by a special agent, with armed guards watching.
"They're treating me like a suspect," he says. "Like while I was in there, I just felt like I was a criminal. At a certain point they almost make you feel like you did something wrong."
Civil liberties groups say U.S. border officials are violating the constitutional rights of American Muslims by asking about their religious beliefs and practices on their return from trips abroad.
Ho and Shibly's testimony form part of a complaint to the government by two groups - the American Civil Liberties Union and Muslim Advocates.
It alleges that the U.S. Customs and Border Protection agency, or CBP, has been questioning Muslims or people that appear to be Muslim about their religious and political beliefs, associations and activities.
Hina Shamsi is director of the ACLU's National Security Project:
"Of course we all recognize that it is the government's job to keep the country safe and secure, and we want it to do that," she said. "But questioning innocent American Muslims about their religious and political beliefs does nothing to make us safer."
She says it also violates the First Amendment of the Constitution, which guarantees religious liberty.
Shamsi says U.S. citizens and residents may only be questioned in this way if there is a reasonable suspicion, based on credible evidence, that a person has engaged in criminal activity. And the faith-related questions have to be relevant, she says.
"It cannot be a dragnet set of questions," she added. "That is simply impermissible and unconstitutional."
In response to questions by the Voice of America about the allegations, CBP says in a statement that it does not select travelers for questioning on the basis of faith or race.
Although the statement does not address the issue of religious questions, it does maintain that a reasonable suspicion is not required for travelers to be stopped and investigated with regard to their citizenship, identity and admissibility into the country.
Since the September 11, 2001 attacks, there has been a fierce debate in America over how to defend against terrorism carried out in the name of Islam - without violating the rights of this country's Muslim minority.
Shibly immigrated to America with his family at the age of four. He says his experience at the airport makes him worry about the future for his one-year-old boy.
"I want him to grow up in the America that I grew up in, where people respect [each other] despite religious and political and ideological differences, and we're all - at the end of the day - Americans, and we love each other and we can all work together toward the common good," said Shibly.