The United States Department of Transportation (DOT) has fined Frontier Airlines (F9, Denver International), American Airlines (AA, Dallas/Fort Worth) and Delta Air Lines (DL, Atlanta Hartsfield Jackson) for violating consumer protection rules. Frontier was hit the hardest with a USD400,000 penalty, while American Airlines and Delta copped USD250,000 and USD200,000 respectively.

Frontier's violations relate to the manner in which it dealt with passengers on overbooked flights and its treatment of passengers with disabilities.

"The Department found that Frontier failed to seek volunteers before bumping passengers involuntarily, failed to provide bumped passengers the required written notice describing their rights, and failed to provide proper compensation to passengers in a timely manner," the DOT said in a statement.

Additionally, adequate wheelchair assistance was not provided to passengers with extra physical needs during enplaning, deplaning, preboarding and moving within the airport.

Delta was fined for underreporting its mishandled baggage reports, while American's offence was failing to process refunds in a timely manner.