(Daniel Acker/BLOOMBERG) 
 
 The Justice Department is investigating whether some of America’s biggest airlines have colluded to keep airfares high, striking at an industry that has posted record profits recently while limiting routes and affordable seats, officials familiar with the matter said Wednesday. Justice Department spokeswoman Emily Pierce confirmed the probe, saying investigators are looking into “possible unlawful coordination by some airlines,” but she would not name the carriers. Representatives from Delta Air Lines, Southwest Airlines, American Airlines and United Airlines confirmed they were among those being investigated and said they were complying with Justice Department requests. “Our members compete vigorously every day, and the traveling public has been the beneficiary.” 
 
 [Airlines are making record profits, but don’t expect a cheaper seat] 
 
 U.S. airlines received a letter Tuesday demanding copies of all communications between carriers, their shareholders and investment analysts about their plans for limiting seat capacity, according to the Associated Press, which first reported the investigation. The average domestic airfare rose 13 percent from 2009 to 2014, when adjusted for inflation, according to the Bureau of Transportation Statistics. And that doesn't include the billions of dollars airlines collect from new fees: $25 each way to check a bag and $200 to change a domestic reservation. The civil antitrust investigation by the Justice Department appears to focus on whether airlines illegally signaled to each other how quickly they would add new flights, routes and extra seats.
– Because extra fees and delayed flights weren't enough reason to sour on airlines, the Justice Department has added one more: Federal investigators suspect that the airlines are colluding to rip off passengers. The Justice Department has launched an antitrust investigation and demanded all communication airlines have had with each other about adding flights, routes, or seats, reports AP. The suspicion is that they're sending each other signals about such things in order to keep seats in short supply and prices high. A Justice Department spokesperson confirmed the investigation, though the airlines aren't named. The Washington Post reports that United is one of them, and both stories point out that United, American, Delta, and Southwest now handle 80% of all domestic passengers, making the other recipients of the feds' letter not hard to guess. One sign that something isn't right: Domestic airfare shot up 13% from 2009 to 2014, after a series of industry mergers.