United Airlines has been ordered to pay more than $US1 million in fines by the US Department of Transport for making passengers wait on stranded planes for more than three hours at Chicago's O'Hare International Airport last year.
The fine comes after new rules introduced in 2010 banned airlines for stranding passengers on the tarmac for more than three hours.
AAP reports the delays involved 13 United planes in July 13, 2012, a stormy day in Chicago which saw the disruption of many flights out of O'Hare.
"It is unacceptable for passengers to be stranded in planes on the tarmac for hours on end," US Transportation Secretary Anthony Foxx said in a statement on Friday.
"We will continue to require airlines to adopt workable plans to protect passengers from lengthy tarmac delays and carry out these plans when necessary."
The department said the airline broke the three-hour rule by as much as an hour and 17 minutes, and failed to contact airport workers or other airlines for assistance.
The airline said it is "committed to complying with the tarmac regulations and we continue to improve or procedures while maintaining the safety of our customers and co-workers”.
The company will pay the US government $US475,000, while $US185,000 will be used to compensate affected passengers.
While US440,000 will go towards the acquisition and maintenance of a surveillance system to monitor the location of each of its planes on the airfield.