United CEO Oscar Munoz doubled down in a letter to employees on Monday evening, claiming that employees "followed established procedures" when removing a passenger from a plane because it was overbooked, and calling the passenger "disruptive and belligerent."



United had to ask several passengers who had already boarded a flight from Chicago to Louisville on Sunday evening to leave, as the airline had sold too many tickets. One man refused to leave, and United called airport officials, who forcibly removed him from the plane.

Video circulated of the incident earlier in the day, showing the man being dragged from the plane and later returning with blood on his face. The incident drew scorn on Twitter and other social media, especially when Munoz used the euphemism "re- accomodate " in a public statement to describe the customers booted from the flight.

According to the letter, which was obtained by CNBC, when crew members first approached the passenger to tell him to leave, he "raised his voice and refused to comply," and each time they asked again "he refused and became more and more disruptive and belligerent."

Crew members "were left with no choice but to call Chicago Aviation Security Officers to assist in removing the customer from the flight," Munoz wrote, and at one point the passenger "continued to resist - running back onto the aircraft in defiance of both our crew and security officials."

Munoz acknowledged to employees that the company could learn lessons from the incident, but said: "I emphatically stand behind all of you."

Here's the video, which went viral earlier today: