A religious rights group filed a complaint Wednesday against Southwest Airlines over an April incident involving a Muslim passenger.

The Council on American-Islamic Relations filed the complaint with the federal Department of Transportation on behalf of Khairuldeen Makhzoomi.

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Makhzoomi was taken off a flight to Oakland at the Los Angeles International Airport for questioning after he made a passing reference to the Islamic State group in Arabic during a phone call. Makhzoomi was talking to his uncle in Baghdad about a speech Makhzoomi had attended by United Nations Secretary General Ban Ki-moon.

Makhzoomi's father was an Iraqi diplomat who was jailed and later killed under Saddam Hussein's regime. His family came to the U.S. in 2010.

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The group said it filed the complaint in order to hold the airline accountable for its actions against Makhzoomi.

Southwest Airlines has investigated the incident as well.

"The internal review determined that it was the content of the conversation, not the language used, that prompted the report leading to the investigation," airline spokeswoman Brandy King said in a statement to The Independent. "Our crew responded by following protocol, as required by federal law, to investigate any potential threat. We regret any less than positive experience a customer has on Southwest. Southwest neither condones nor tolerates discrimination of any kind."