United Airlines was fined $2.75 million by the U.S. Transportation Department for violating rules governing tarmac delays and the assistance of passengers with disabilities, the agency said on Thursday.

The department said in a statement that United, the second-largest U.S. carrier, at times did not return wheelchairs to customers promptly or give them adequate help moving through five of its hub airports in 2014.

In addition, severe weather in December 2013 and May 2015 led United to violate a rule that requires airlines to offer passengers the chance to deplane after a tarmac delay of more than three hours on U.S. domestic flights, the agency said.

“We remain committed to fully meeting all (Transportation Department) rules – particularly during difficult operating conditions,” a spokesman for parent United Continental Holdings Inc said in a statement.

Rival airlines have committed similar violations in past years. Southwest Airlines Co was fined $1.6 million in 2015 for breaking the tarmac-delay rule, and US Airways, now part of American Airlines Group Inc, received a $1.2 million fine in 2013 for offering inadequate wheelchair assistance at two airports.

United has agreed to apply $375,000 of its fine toward plane parking systems that could help reduce taxi times during winter storms, the U.S. agency said.

It also will apply $500,000 of the fine toward expanding its mobile application to let customers make disability-related requests, the regulator said.

“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,” Jon Roitman, senior vice president of airport operations at United, said in an online posting on Thursday.