An architect of Iraqi descent has said he was forced to remove a T-shirt that bore the words "We will not be silent" before boarding a flight at New York.
A demonstrator wears a similar T-shirt at a New York protest in July
Raed Jarrar said security officials warned him his clothing was offensive after he checked in for a JetBlue flight to California on 12 August.
Mr Jarrar said he was shocked such an action could be taken in the US.
US transport officials are conducting an inquiry after a complaint from the US Arab Anti-Discrimination Committee.
JetBlue said it was also investigating the incident but a spokeswoman said: "We're not clear exactly what happened."
Mr Jarrar's black cotton T-shirt bore the slogan in both Arabic and English.
He said he had cleared security at John F Kennedy airport for a flight back to his home in California when he was approached by two men who wanted to check his ID and boarding pass.
Mr Jarrar said he was told a number of passengers had complained about his T-shirt - apparently concerned at what the Arabic phrase meant - and asked him to remove it.
He refused, arguing that the slogan was not offensive and citing his constitutional rights to free expression.
Mr Jarrar later told a New York radio station: "I grew up and spent all my life living under authoritarian regimes and I know that these things happen.
"But I'm shocked that they happened to me here, in the US."
After a difficult exchange with airline staff, Mr Jarrar was persuaded to wear another T-shirt bought for him at the airport shop.
"We Will Not Be Silent" is a slogan adopted by opponents of the war in Iraq and other conflicts in the Middle East.
It derives from the White Rose dissident group which opposed Nazi rule in Germany.