In the video, 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.
Other passengers 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 $400 and then $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.
In the process, the man's glasses were knocked off and he was hauled down the aisle by stewards after the man refused to give up his seat to allow stand-by aircrew to take it.
"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."
The incident ignited social media outrage, with "United" a trending term on Twitter, Facebook and Google.
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 $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.
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 $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 $1,350, for longer delays.
When they bump passengers, airlines are required to give those passengers a written description of their compensation rights.