The Department of Justice has issued subpoenas to a number of major airlines as part of an investigation into “possible unlawful coordination” that would’ve enabled airlines to keep ticket prices artificially high.

The Associated Press reports which airlines are suspected of misconduct:

American Airlines, Delta Air Lines, Southwest Airlines and United Airlines all said they received a [subpoena] letter and are complying. Several smaller carriers, including JetBlue Airways and Frontier Airlines, said they had not been contacted by the government.

The airlines received the letter from the DoJ requesting “copies of all communications” made between airlines and analysts regarding intentions to control seat capacity. Per CNN, investigators are reviewing “public comments by airline executives and industry analysts.”

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As the number of airlines in the United States has decreased over the years through mergers and acquisitions, the number of airline choices available to consumers has similarly decreased. This has given the remaining airlines greater market share than ever before and more power to work together to maintain high ticket prices. For well over a decade, ticket prices have increased despite a downward trend in fuel costs which could indicate a move that is anti-consumer and free-trade.

Photo credit: Passengers with luggage - Mel Evans/AP

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