“As part of the probe, U.S. Secretary of Transportation Pete Buttigieg sent letters to American Airlines, Delta Air Lines, Southwest Airlines, and United Airlines ordering them to provide records and submit reports with detailed information about their rewards programs, practices, and policies,” the agency said in a statement announcing the action. “DOT’s probe is focused on the ways consumers participating in airline rewards programs are impacted by the devaluation of earned rewards, hidden or dynamic pricing, extra fees, and reduced competition and choice.”