The Chicago-headquartered airline's share price fell sharply during trading on the morning of 11 April, but largely recovered during the afternoon.
A Chicago alderman said representatives from United Airlines and the city Aviation Department have been summoned by his committee to answer questions about Sunday's incident.
United Airlines CEO Oscar Munoz says the company will review its policies.
"You saw us at a bad moment", he said. Like you, I continue to be disturbed by what happened on this flight and I deeply apologize to the customer forcibly removed and to all the customers aboard.
The CEO vowed to never again let a law enforcement remove "a booked, paid, seated passenger", from a plane. "We can't do that".
All passengers on the flight will now be offered compensation amounting to to the full cost of their ticket, which they can claim in the form of cash, travel credits or miles.
Likewise, the Chicago Aviation Department has said only that one of its employees who removed Dao did not follow proper procedures and has been placed on leave.
Meanwhile, the Chicago Department of Aviation is investigating the Chicago Aviation Security Office, who have flown remarkably under the radar during all of this. "I kind of doubt it I have yet to find his email because I would like to send him all the emails that I've received on his behalf", San Antonio's Munoz said.
Munoz said the incident on Sunday (Monday NZT) resulted from a "system failure" that prevented employees from using "common sense" in the situation and that Dr David Dao, whom security officers pulled by his hands from the cabin before takeoff, was not at fault.
It was at least Munoz's fourth statement about the confrontation.
"He was approached a few more times after that in order to gain his compliance to come off the aircraft and each time he refused and became more and more disruptive and belligerent". He acknowledged that Sunday evening's event make passage of that proposal much tougher. "That's my promise", said Mr Munoz. Dao, a physician specializing in pulmonary disease, lives in Elizabethtown, Kentucky.
Dao's attorneys filed a petition with the Cook County Circuit Court Wednesday requesting to preserve all potential evidence from the flight, including surveillance video recordings showing passengers boarding the plane.
A spokeswoman for Dao's attorneys told BuzzFeed News it was "premature" to discuss anything about a potential lawsuit, but added that his lawyers would talk about the case during a news conference scheduled for Thursday morning.
French Socialist candidate holding Paris rally
Until now, Le Pen had struggled to get the campaign to focus on her party's trademark tough security and immigration stance. The months-long French campaign seemed to grow ever weirder and more uncertain as polling day approached.