IBM is facing an investigation from Depatment of Justice (US) for its competition killing practices in Mainframe space. Earlier IBM used to license its Mainframe software to be run on Non IBM hardware, but sometime back IBM withdrew such offers and now completely dominates the hardware segment of Mainframes.
Also one more claim is that since many Major clients have written complex business code on Mainframes and IBM has made it very difficult to port these applications to another vendor say Oracle or Microsoft.
T3T a smaller company is pursuing a case against IBM in this regard but was rejected by the court recently. But now Justice department has taken the matter. Earlier Platform Solutions sued IBM but later was purchased by IBM and hence ending any chance of legal battle.