The Department of Justice has launched an investigation into possible antitrust practices including controlling the supply of available seats and price-fixing at the four biggest airline carriers in the United States: American Airlines Group Inc., United Continental Holdings Inc., Delta Air Lines Inc., and Southwest Airlines Co. according to several reports.

Airline passengers filed class action lawsuits against these carriers for unfair pricing practices as the investigation by the Department of Justice began. Passengers claim the consolidation of airline carriers has reduced the capacity of seats on flights which increases ticket prices as well as created an atmosphere which allows for price-fixing as these four carriers make up 80% of the domestic airline market.