The U.S. Department of Transportation has determined that Southwest Airlines improperly compensated travelers who were not able to board flights because of overbooking. They imposed on Southwest a $200,000 fine for bumping passengers without following federal guidelines.

Federal law requires that airlines must offer passengers a voucher for another flight or cash compensation, or both, when the passenger holds a ticket for a flight and is denied a seat because the flight is overbooked. The airline is required to give a written statement explaining their rights to passengers who are involuntarily bumped from a flight. An investigation conducted by the U.S. Department of Transportation found that in 2009 there were ‘numerous instances’ in which Southwest Airlines failed to follow those guidelines by failing to give passengers the required written statement of their rights and failing to inform passengers that they were entitled to cash instead of a voucher for another flight or failed to pay bumped passengers the appropriate sum of money.

Airlines are allowed to book more passengers than the number of seats on a flight to compensate for people who miss the flight or just don’t show up. However, they are required to compensate ticket-holding passengers who are denied boarding because of the practice of overbooking flights.

A spokesperson for the Department of Transportation declined to comment on the number of cases that were investigated, but did say that the airline agreed to pay the $200,000 fine in order to avoid litigation. On the other hand, Brandy King, a Southwest spokesperson, said that the violations occurred only on a small percentage of flights and that the airline is working to improve procedures to reduce an such incidents in the future.

The Southwest $200,000 fine for bumping passengers without following federal guidelines can be waived if the airline stays in compliance over the next year. Southwest Airlines is the second-busiest airline in the U.S. in terms of the number of passengers served annually. The airline is headquartered out of Dallas, Texas.