The U.S. Transportation Department fined the United Airlines $2.75 million for violating rules that protect disabled passengers and rules governing tarmac delays.

According to the International Business Times, the second largest US carrier acknowledged the fine and promised to enhance infrastructure for passengers with disability. The Department of Transportation (DOT) received a lot of complaints last year on mistreatment of passengers with disability.

One of the major incidents that caught the public's eye involves a passenger suffering cerebral palsy who was forced to crawl out of the flight in October, since the crew didn't provide a wheelchair for the person.

"It is our duty to ensure that travelers with disabilities have access to the services they need, and that when significant tarmac delays happen, travelers are not left on the plane. We will make sure that airlines comply with our rules and treat their passengers fairly," said US Transportation Secretary Anthony Foxx.

Daily News reported that the airline also violated a rule that should let passengers deplane due to a tarmac delay of not less than three hours on domestic flights in the US.

This happened during December 2013 and May 2015 when the airline faced severe weather. A United Continental Holdings Inc spokesman said, "We remain committed to fully meeting all (Transportation department) rules - particularly during difficult operating conditions."

USA Today reported that United gets a million requests for wheelchair assistance every year. According to the airlines, it strives to provide the best service possible, but passengers are now asking for better treatment.

The airline said in a blog post, "We want you to know that providing convenient, comfortable and flyer-friendly service to all of our customers is one of our top priorities."

United isn't the only airline that committed such violations. Rival Southwest Airlines Co was also fined with $1.6 million back in 2015 for violating the tarmac-delay rule. US Airways, which is now part of the American Airlines Group Inc, was also fined with $1.2 million in 2013 for providing inadequate wheelchairs.