The Department of Transportation has launched an investigation into the rewards programs of the nation’s four largest airlines, seeking to scrutinize how these programs affect consumers.

The airlines — Delta, American, United, and Southwest — have been instructed to submit detailed reports on their rewards programs within 90 days. The reports will help the government understand issues such as the devaluation of earned rewards, hidden or dynamic pricing, extra fees, and the effects on competition and consumer choice.

The probe marks the first comprehensive government review of the lucrative programs, which generate billions of dollars in revenue annually for the airlines — sometimes surpassing earnings from flight operations. The potential outcomes of the investigation are unclear, but federal regulators could impose changes that might disrupt these profit centers for both airlines and credit card companies, possibly affecting a travel option cherished by many passengers, Bloomberg News reported.

The probe will require the carriers to provide extensive data on their rewards programs, including credit card, consumer incentive, loyalty, and frequent flier programs. Information on any changes made over the past six years, customer complaints, and the impact of mergers on these programs.

“Many Americans view their rewards points balances as part of their savings,” the transportation secretary, Pete Buttigieg, said in a statement. “But unlike a traditional savings account, these rewards are controlled by a company that can unilaterally change their value.”

Airlines for America, a trade group representing major U.S. carriers, defended the programs. “US carriers are transparent about these programs, and policymakers should ensure that consumers can continue to be offered these important benefits,” the group said in a statement.