WATCH: Passengers horrified as security officers drag a screaming man off overbooked United flight

United Airlines is coming under heavy criticism after it had security officers forcibly remove a passenger from an overbooked flight.

A series of videos posted on social media show security officers asking a passenger who was on a Sunday United flight from Chicago to Louisville to leave the plane.

When the man refused, the officers reached in and did something to cause the man to shout out in pain. Afterward, the officers dragged the man off the plane as horrified passengers yelled that there was no need to resort to such force.

In a statement provided to NBC News, United explained that the plane's crew initially looked for people to leave the flight voluntarily because the flight had been overbooked. When no one volunteered, they chose a passenger to be removed, and he refused to cooperate, which forced the crew to call law enforcement officials.

The airline apologized for overbooking the flight but did not apologize for having security drag the passenger off the plane.

Nonetheless, several passengers were visibly disturbed that the airline would resort to such tactics.

Audra Bridges, a passenger who posted a video of the encounter on her Facebook page, was outraged by the way the man was removed.

"They randomly selected people to kick off so their standby crew could have a seat," she wrote. "This man is a doctor and has to be at the hospital in the morning. He did not want to get off. We are all shaky and so disgusted."

An eyewitness similarly tells theLouisville Courier Journal that the passenger told security officers that he was a doctor who needed to see patients of his the next morning.

This didn't convince security officers, however, and she tells the Courier Journal that "a third security official came on the plane and threw the passenger against the armrest before dragging him out of the plane."

"The man was able to get back on the plane after initially being taken off – his face was bloody and he seemed disoriented," the witness tells the Courier Journal.

Watch two videos of the incident below.