The U.S. Department of Transportation will fine American Airlines, Delta Air Lines and Frontier Airlines for violating various Consumer Protection Rules. The total fine amounts to $850,000.

The biggest fines are imposed on Frontier Airlines, which received a $400,000 ticket for “violating the Department’s oversales and disability rules.” The DOT said the airline failed to ask for volunteers before involuntarily bumping passengers and for failing to provide the bumped passengers with a written notice with their rights. The airline also failed to pay the proper compensation to these passengers in a timely manner.

The airline was also penalized for not providing passengers with adequate wheelchair assistance during boarding, deplaning and in the terminal. It also did not adequately respond to complaints filed by disabled passengers.

American Airlines was fined $250,000 for having “failed to process refund requests in a timely manner.” Delta must pay $200,000 for filing inaccurate baggage reports with the DOT.

“The underreporting made Delta’s ranking in the Department’s Air Travel Consumer Report seem better than it was at various times,” said the DOT press statement.