IBM is being investigated after suspicions that the IT giant has “abused its dominance of the mainframe business to squeeze rivals”.
The US Department of Justice is pursuing the matter after being urged by The Computer and Communications Industry Association (CCIA).
The CCIA, a not-for-profit trade body, has levelled a number of accusations at IBM.
It believes the computer group has unfairly withdrawn licenses for its operating systems from customers who use non-IBM hardware.
It says that IBM has unfairly blocked its licence to users of ‘rival-friendly’ open-source software Hercules.
Hercules allows IBM's mainframe operating systems to run on Intel and AMD-based PCs.
It also believes IBM is retaliating against business partners which it brands disloyal, and had acquired rival group PSI to stifle competition.
IBM denies the accusations and will co-operate with any investigations.
The CCIA’s trade membership includes many giants of the IT industry, including Microsoft, yet IBM is not a member.