(CNN) -- Two imams heading to a conference on prejudice against Muslims said they were forced off their North Carolina-bound flight to undergo an additional security check -- only to have the pilot take off without them, even after they were cleared.

Atlantic Southeast Airlines said in a statement that it was investigating the incident, which took place Friday night aboard a flight out of Memphis, Tennessee.

Masudur Rahman and Mohamed Zaghloul, both imams in the Memphis area, were clad in Islamic attire when they were told to leave the aircraft as it was taxiing toward the runway. Their lawyer, Mo Idlibi, told CNN on Saturday that neither man had done anything out of the ordinary, nor were they praying or chanting.

Rahman, who is also a professor of Arabic at the University of Memphis, said he and his colleague cooperated throughout the process and thanked Transportation Security Administration agents and others for their kindness and courtesy. But he said, through intermediaries, that they had difficulty finding out why they were ever kicked off the plane.

One representative of Delta Air Lines, who claimed to be advocating on the two men’s behalf, came out visibly red-faced after a long talk with the pilot, according to Rahman. This was after the plane had returned to the gate and Rahman and Zaghoul had gotten off and gone through a secondary screening process. Shortly thereafter, the plane took off -- without the men, who hadn’t been allowed back on board.

“He didn’t give any reason,” said Rahman, referring to the pilot. “(The representative) said only that the pilot is not allowing you to go.”

Atlantic Southeast Airlines, which runs Delta Connection and United Express flights, apologized “for any inconvenience that this may have caused.”

Atlantic Southeast did not say why the two men were taken off the flight, but did claim they were given the opportunity to fly on a different flight.