'It's us against them': The man dragged from a United flight is prepping for a legal battle against the airline

David Dao, the 69-year-old man who sparked public outcry after being forcibly removed from a United Airlines flight, is prearing to file a lawsuit against the airline.

The announcement was made during a Thursday press conference with Dao's lawyer, Tom Demetrio, and one of his daughters, Crystal. Demetrio said the lawsuit will serve to "stand up for passengers going forward."

"They have treated us less than we deserve," Demetrio said of airline carriers in general.

"It's us against them. Well we're them and this lawsuit, among other things, hopefully will create not just a national discussion, but international discussion, on how we're going to be treated going forward," Demetrio continued.

Dao took his first steps toward filing the lawsuit on Wednesday when he issued an order with the city of Chicago and United asking to keep all footage, audio recordings, and any other reports and material from the flight.

A video went viral Monday showing Dao being dragged by police officers off a plane traveling from Chicago to Louisville.

The incident occurred after United asked volunteers to give up their seats to make room for four crew members on the full flight in exchange for $1,000. When no one volunteered, United selected four passengers to give up their seats, but Dao refused, saying he was a doctor and had to see patients the next morning.

United then called three police officers from the Chicago Department of Aviation to remove Dao from the plane. Dao was treated at a local hospital for injuries he suffered after being dragged off the plane.

The three police officers involved in the incident have been placed on leave, and the government is now reviewing the events that transpired.

United referred to its "Contract of Carriage" to remove Dao from the flight, which passengers agree to whenever they buy a ticket with the airline. The contract says United can deny passengers from boarding if a flight is overbooked and no one volunteers to give up their seat.

In Dao's case, United invoked its "involuntary boarding" policy after all the passengers had boarded the plane. United told Business Insider boarding refers to any period before the flight physically takes off.

This story is developing...