United Airlines has been fined $2.75 million by the U.S. Department of Transportation over accusations that it failed to adhere to rules aimed at protecting disabled passengers and preventing excessive tarmac delays, the agency said Thursday.

The DOT revealed in a press release that the bulk of the fine, $2 million, relates to the treatment of disabled passengers. It alleges that United Airlines, the second- largest U.S. carrier, failed to return passengers' wheelchairs, other mobility aids, or other assistive devices "in a timely manner or in the condition in which the airline received them."

One such example was in October when a passenger with cerebral palsy was forced to crawl out of the plane since the airline crew failed to provide him with a requested special wheelchair that fits in the aisle.

As for tarmac delays, severe weather led to one incident at Houston's William P. Hobby Airport in May 2015 and five at Chicago's O'Hare International Airport in December 2013 that caused United to violate a rule that requires airlines to offer passengers the chance to deplane for more than three hours on U.S. domestic flights, according to the Associated Press.

Other cited airports include Denver International Airport, Newark Liberty International Airport and Washington's Dulles International Airport.

United said in a statement that it remains committed to meeting all DOT rules.

"We want you to know that providing convenient, comfortable and flyer-friendly service to all of our customers is one of our top priorities, and we are committed to meeting all DOT rules," United said in a blog post Thursday on its website, according to USA Today. "And while we've made significant efforts to improve, we remain focused on doing better."

The airline has also agreed to apply $375,000 of the fine toward plane parking systems aimed at helping reduce taxi times during winter storms and an additional $500,000 of the fine toward developing better technology to assist passengers through the airline's mobile app. The agreement requires both steps to be completed by Sept. 1, 2017.

"We expect this to greatly improve our ability to have wheelchairs where they need to be, when they need to be there, so that our customers can get on their way home or to their next destination with ease," said Jon Roitman, United's senior vice president of airport operations.