The U.S. Department of Transportation is reviewing United Airlines' widely criticized handling of a passenger who was forcibly removed from a plane that had been overbooked.

A group of lawmakers also is calling for a congressional investigation into the case, as well as a closer look at the policies of airlines when a flight is at capacity.

United has come under fire after a 30-second video taken by a fellow passenger on the flight from Chicago to Louisville went viral late Sunday.

A 69-year-old Asian man was shown being dragged out of the plane. He went to the hospital for injuries on his face. Since then, one of the officers involved in the incident has been put on leave.

Specifically, the DOT is looking into whether United 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,” the Transportation Department said in a statement. “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."

The incident prompted Eleanor H. Norton, a non-voting House Democrat, to call for congressional hearings:

“I deplore #UnitedAirlines for abusive removal of passenger from flight. I’m requesting @Transport hearing on this & other similar incidents.”

Norton, a senior member of the House Transportation and Infrastructure Committee, wants a hearing that would allow lawmakers “to question airport police, United Airlines personnel, Federal Aviation Administration officials, and airport officials, among others, about whether appropriate procedures were in place in Chicago and are in place across the United States when passengers are asked to leave a flight.”

“Airline passengers must have protections against such abusive treatment,” Norton said.

Reps. Jan Schakowsky, D-Ill., and Brendan Boyle, D-Pa., also decried the passenger’s treatment, with Boyle joining Holmes in calling for an investigation.

“I will not fly #United anymore. Further, it’s time for govt to investigate their repeated abuses toward passengers,” Boyle tweeted.

Sen. Chris Van Hollen, D-Md., also called for a “full investigation.” And New Jersey Democratic Sen. Robert Menendez called the incident “disturbing” and called a statement by United’s CEO Oscar Munoz an “empty promise” that missed the mark.

Munoz publicly apologized “for having to re-accommodate these customers” without detailing any policy changes. It’s the second time in less than a month that United has been the subject of negative headlines. The airline was slammed for not allowing two teenage girls to wear leggings on board. United claimed it was a violation of a dress code for employees and guests traveling with them.

In Sunday’s incident, cellphone footage shows security officers and police pulling the man from his seat to the floor. The passenger looks unconscious as other horrified passengers are shown screaming for the police to stop. Later footage shows the man bleeding from his face.

White House spokesman Sean Spicer weighed in Tuesday afternoon and said it was "troubling" to see how the situation had been handled.

"I don't know that anyone looks at that video and isn't a little disturbed that another human being is treated that way," Spicer said.

United has defended its actions. Airlines are allowed to oversell flights. Last year, airlines in the U.S. booted 40,000 passengers from their seats.

That number does not include passengers who volunteered to give up their seats. According to government statistics, 434,000 people voluntarily gave up their seats on the country’s 12 largest airlines in exchange for travel vouchers or other rewards including an upgrade on another flight.

When no one volunteers, airlines can deny boarding or bump passengers. Airlines are required to give those customers a written statement that explains why as well as their compensation.