Why this is an accusation as versus a simple description of the competitive process is explained in Dominick Armentano's outstanding new book: Antitrust: The Case for Repeal. It is now available for on-line orders from Mises.org. Another option is to purchase it from Amazon.com
This newly revised 2nd edition deals with the Microsoft, Toys `R' Us, and many other recent cases, and explains the absurdities inherent in these government complaints of "predatory pricing." His recommendation: abolish all antitrust regulation.
Also read an interview with Professor Armentano in the Austrian Economics Newsletter.