U.S. probing possible collusion by airlines to keep fares high by Reuters @FortuneMagazine July 1, 2015, 2:31 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons The Justice Department is investigating whether U.S. airlines are working together to keep ticket prices high, spokeswoman Emily Pierce said on Wednesday. The Associated Press, which broke the story, said that the department was trying to determine whether the airlines were colluding to grow slowly in a bid to keep airfares high. “We are investigating possible unlawful coordination by some airlines,” said Pierce in a statement. As a result of a series of mergers starting in 2008, American Airlines AAL , Delta Air Lines DAL , Southwest Airlines LUV and United Airlines UAL now control more than 80% of the seats in U.S. skies, the AP reported. Those airlines have cut unprofitable flights, filled a higher percentage of seats on planes, and have worked to slow growth in order to command higher airfares, said the AP.