02:22 PM EDT, 09/05/2024 (MT Newswires) -- The US Department of Transportation launched an investigation on Thursday into the rewards programs of the four largest US airlines.

US Secretary of Transportation Pete Buttigieg sent letters to Delta Air Lines ( DAL ) , American Airlines ( AAL ) , United Airlines (UAL) and Southwest Airlines ( LUV ) ordering them to provide records and submit reports with information on their rewards programs, policies and practices.

The regulator's investigation is concentrated on the ways participants in airline rewards programs are affected by the devaluation of earned rewards, hidden dynamic pricing, additional fees and diminished competition and choice, the Department of Transportation said.

Delta, American, United and Southwest ( LUV ) did not immediately reply to requests for comment from MT Newswires.

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