WASHINGTON (Reuters) - The Department of Transportation fined Delta Air Lines Inc $2 million for violating federal rules on passengers with disabilities, the agency said on Thursday.

The fine is the largest ever imposed against an airline in a case not related to safety.

The DOT said it had found many violations of the requirements, in 2007 and 2008, to provide assistance to passengers while getting on and off airplanes.

The government also found Delta frequently did not respond adequately to disability complaints from passengers.

Delta agreed to settle the case without admitting wrongdoing.

Most of the fine can be used by the airline to improve its service for travelers with disabilities, especially those in wheelchairs.

Delta said in a statement it has made "significant investments" to address the issue since it was raised and would "continue to coordinate" with regulators.

The airline was cited by regulators for similar violations in 2003.

(Reporting by John Crawley; Editing by Lisa Von Ahn and Gerald E. McCormick)