Video footage shows a man and a member of staff at the airline’s subsidiary United Ground Express squaring off at the check in desk at Newark Liberty International Airport in New Jersey. The worker appears to slap the passenger in the face before he lashes out in retaliation.
The passenger then appears to throw several punches, pushing the worker off balance before he falls backwards over the check in desk.
A woman can be heard in the background, crying out, “Stop, please stop”, as the tussle takes place.
The worker stumbles to his feet while the passenger walks off. The man can be heard saying: “You want some more? You want more?”
It is not known what caused the fight to erupt but details of the incident have been passed to law enforcement.
A United Airlines spokesperson said: “United Airlines does not tolerate violence of any kind at our airports or on board our planes and we are working with local authorities to further investigate this matter.”
Further footage shows the man throwing punches at the worker before he strikes back.
The videos emerged days after a Jet2 plane from Gran Canaria heading for Newcastle was diverted to Porto in Portugal because of a disruptive passenger.
Jet2 said at the time: “We can confirm that flight LS542 from Gran Canaria to Newcastle diverted to Porto this morning so that a disruptive passenger could be offloaded.
“As a family-friendly airline, we take a zero-tolerance approach to disruptive behaviour.
“We will not hesitate to vigorously pursue any costs incurred as a result.”
That incident also came after Jet2 banned two brothers from the airline for life and issued them with a £50,000 bill.
In a statement, Jet2 said Alfie and Kenneth Springthorpe, from Sidcup, southeast London, “displayed a catalogue of appalling behaviour” during a flight from Stansted to Crete.
A Jet2 spokesperson said the plane diverted to Corfu after the pair became aggressive, violent and caused damage to the aircraft.