By Kelly Werthmann

DENVER (CBS4)– A man was violently dragged off a United Airlines flight in Chicago on Sunday night, after the flight was overbooked and the passenger refused to give up his seat.

Other passengers on board the Louisville bound flight captured the incident on camera, and those videos have gone viral.

Passenger Audra D. Bridges posted the video on Facebook after the incident Sunday evening. It shows the guards grabbing the screaming man from a window seat and pulling him across the armrest before dragging him down the airplane aisle by his arms.

“No! This is wrong! Oh my God, look what you did to him!” one passenger screams in the video.

Bridges said United Airlines needed four seats for its standby crew. When passengers didn’t accept the $800 and hotel offer from the airline, United began involuntarily bumping passengers.

“Certainly you can be involuntarily bumped,“ aviation attorney Joseph LoRusso told CBS4’s Kelly Werthmann. “Can you be forcibly removed in a situation like this? That’s where we get into a bit of a gray area.”

LoRusso said federal law allows airlines to involuntarily remove passengers from overbooked flights, with compensation. Passengers have the right to refuse, LoRusso added, but if a person does not comply with airline instructions, federal law does permit the airline to ask authorities to remove the passenger from the plane.

Passenger Jayse D. Anspach posted the video of the man being forcibly removed from his seat on his Twitter account.

@United overbook #flight3411 and decided to force random passengers off the plane. Here's how they did it: pic.twitter.com/QfefM8X2cW — Jayse D. Anspach (@JayseDavid) April 10, 2017

“To the extent this was taken, that creates an entirely different subject of whether it was overly forceful or beyond protocol,” he said.

However, LoRusso questions if United Airlines was within its legal right to ask flight 3411 passengers for their seats because standby crew should not have priority over paying customers.

“Were we really dealing with selling more tickets than we had seats? It doesn’t seem like that’s the case, at which point the overbooking protocol seems to be unwarranted,” LoRusso said.

United Airlines said they are investigating the incident and are working with the passenger who was removed.

As for future passengers, LoRusso recommends travelers know they have rights on the ground and in the air and take a closer look at the U.S. Department of Transportation’s Passenger Bill of Rights.

According to businessinsider.com, United CEO Oscar Munoz wrote an open letter to the airline’s employees saying they can learn from the incident but didn’t offer an apology.

“I do … believe there are lessons we can learn from this experience, and we are taking a close look at the circumstances surrounding this incident. Treating our customers and each other with respect and dignity is at the core of who we are, and we must always remember this no matter how challenging the situation,” Munoz said in the letter.

The Department of Transportation provided CBS4 the following statement:

“The Department of Transportation (USDOT) remains committed to protecting the rights of consumers and is reviewing the involuntary denied boarding of passenger(s) from United Express flight 3411 to determine whether the airline complied with the oversales rule. The Department is responsible for ensuring that airlines comply with the Department’s consumer protection regulations including its oversales rule. While it is legal for airlines to involuntary bump passengers from an oversold flight when there are not enough volunteers, it is the airline’s responsibility to determine its own fair boarding priorities.”

Kelly Werthmann joined the CBS4 team in 2012 as the morning reporter, covering national stories like the Aurora Theater Shooting and devastating Colorado wildfires. She now anchors CBS4 Weekend Morning News and reports during the week. Connect with her on Facebook or Twitter @KellyCBS4.