CHICAGO — Video of police officers dragging a passenger from an overbooked United Airlines flight sparked an uproar Monday on social media, but United’s CEO defended his employees, saying they followed proper procedures and had no choice but to call authorities and remove the man.

As the flight waited to depart from Chicago’s O’Hare Airport, officers could be seen grabbing the screaming man from a window seat, pulling him across the armrest and dragging him down the aisle by his arms. United was trying to make room for four employees of a partner airline on the Sunday evening flight to Louisville, Kentucky.

Other passengers on Sunday night’s United Express Flight 3411 are heard saying, “Please, my God,” ”What are you doing?” ”This is wrong,” ”Look at what you did to him” and “Busted his lip.”

Passenger Audra D. Bridges posted the video on Facebook. Her husband, Tyler Bridges, said United offered USD$400 and then USD 800 vouchers and a hotel stay for volunteers to give up their seats. When no one volunteered, a United manager came on the plane and announced that passengers would be chosen at random.

“We almost felt like we were being taken hostage,” Tyler Bridges said. “We were stuck there. You can’t do anything as a traveler. You’re relying on the airline.”

Oscar Munoz, CEO of United Airlines’ parent company, apologized first in a written statement and then in a letter to employees Monday evening.

Munoz said he was “upset to see and hear about what happened” at O’Hare. He added, however, that the man dragged off the plane had ignored requests by crew members to leave and became “disruptive and belligerent,” making it necessary to call airport police.

“Our employees followed established procedures for dealing with situations like this,” Munoz told employees. “While I deeply regret this situation arose, I also emphatically stand behind all of you, and I want to commend you for continuing to go above and beyond to ensure we fly right.”

Munoz said that the airline might learn from the experience, and it was continuing to look into the incident.

The flight was operated for United by Republic Airline, which United hires to fly United Express flights. Munoz said four Republic employees approached United’s gate agents after the plane was fully loaded and said they needed to board. He said the airline asked for volunteers to give up their seats, and then moved to involuntary bumping, offering up to USD $1,000 in compensation.

The passenger who refused to leave told the manager that he was a doctor who needed to see patients in the morning, Tyler Bridges said.

“He was kind of saying that he was being singled out because he’s a Chinese man” when speaking to the manager, who was African-American, Bridges said.

“You should know what this is like,” the man said, according to Bridges.

The AP was unable to confirm the passenger’s identity.

Two officers tried to reason with the man before a third came aboard and pointed at the man “basically saying, ‘Sir, you have to get off the plane,'” Bridges said. That’s when the altercation happened.

One officer involved has been placed on leave, the Chicago Aviation Department said.

After the passenger was removed, the four airline employees boarded the plane.

“People on the plane were letting them have it,” Bridges said. “They were saying, ‘You should be ashamed to work for this company.'”

A few minutes after the employees boarded, the man who was removed returned, looking dazed and saying he had to get home, Bridges said.

In a video, the man can be seen standing in the aisle near what appears to be the rear of the aircraft. Blood is on his mouth, chin and cheek as he said, “I want to go home.”

Officers followed him to the back of the plane. Another man traveling with high school students stood up at that point and said they were getting off the plane, Bridges said.

About half of the passengers followed before United told everyone to get off, he said.

The man who was originally dragged down the aisle was removed from the plane again, and United employees made an announcement saying they had to “tidy up” the aircraft, Bridges said.

Bridges’ wife told him she saw the man taken away on a stretcher, he said.

After a three-hour delay the flight took off without the man aboard, Bridges said. A United employee apologized to passengers, he said.

Airlines are allowed to sell more tickets than there are seats on the plane, and they routinely overbook flights because some people do not show up.

It’s not unusual for airlines to offer travel vouchers to encourage people to give up their seats, and there are no rules for the process. When an airline demands that a passenger give up a seat, the airline is required to pay compensation of double the passenger’s one-way fare, up to USD $675, if the passenger can be placed on another flight that arrives one to two hours later than the first flight, or four times the ticket price, up to USD $1,350, for longer delays.

When they bump passengers, airlines are required to give those passengers a written description of their compensation rights.

United spokesman Charles Hobart declined to say how the airline compensated the passengers who were forced to leave the plane, saying he did not have those details from employees on the scene.

Bridges said United should not have boarded the flight if it was overbooked.

“The man handled it wrong,” he said. “The police were kind of put in a bad spot. There’s a lot of ways United could have handled it, and that was not one of the good ways.”

Story: Caryn Rousseau and David Koenig