A Muslim passenger was asked to leave an American Airlines plane after a flight attendant told him over the plane's public address system: "I will be watching you."
Mohamed Ahmed Radwan had boarded the flight from Charlotte, North Carolina, to Detroit, Michigan, last December when the announcement was made.
The Council on American-Islamic Relations (CAIR) has now filed a complaint to the US Department of Transportation, accusing American Airlines of "discriminatory conduct".
A letter from CAIR staff attorney Maha Sayed dated July 20 says: "As Mr Radwan took his designated seat, a female flight attendant loudly announced: 'Mohamed Ahmed, seat 25-A: I will be watching you'.
"The flight attendant was positioned in the aisle towards the rear of the plane and passengers in the vicinity heard her statement.