The U.S. Department of Transportation (DOT) has fined Spirit Airlines $100,000 for failure to properly record and respond to complaints about its treatment of passengers with disabilities, which resulted in an undercount of those complaints to the DOT.

“Our rules on how airlines handle disability-related complaints are designed to help us ensure that passengers with disabilities are treated fairly when they fly,” said Transportation Secretary Ray LaHood. “We will continue to make sure carriers comply with our disability rules and take enforcement action when they do not.”

Spirit is currently running an aggressive campaign in which it claims that new DOT rules designed to provide new protections to airline consumers require airlines to “hide taxes” that are included in airfares. DOT has denied those claims.

DOT prohibits discrimination in air travel on the basis of disability. Under DOT rules, carriers must sort disability-related complaints into categories based on the type of disability and nature of the complaint, and submit an annual report to the department on disability complaints received in the previous year. Each issue raised in a complaint must be recorded separately to account for the total number of complaints a carrier receives.

DOT compiles these reports and then publishes them so consumers can compare carriers. In addition, if an airline receives a written complaint alleging a violation of the department’s disability rules, the carrier must provide a written response within 30 days that specifically discusses the complaint, gives the carrier’s view of whether a violation occurred, and states that the complaint may be referred to DOT for an investigation.

DOT reviews found that Spirit violated these rules by failing to adequately categorize and account for all the disability-related issues that were raised in complaints received during 2009, leading to an undercounting of the actual number of complaints in the carrier’s annual report to DOT. Many issues raised in the complaints were not separately counted, and a large number of additional complaints were not accounted for, DOT’s Enforcement Office found. In addition, Spirit failed to provide adequate responses to a vast majority of the disability-related complaints it received in 2009 and 2010.