The US Department of Justice (DoJ) is investigating IBM's dominance of the mainframe computer market.
The move comes after the Computer and Communications Industry Association complained about the tactics used by IBM to keep its mainframe customers captive.
Mainframe computers and the associated software and services are still an important source of revenue for IBM.
The Computer and Communications Industry Association (CCIA) alleges IBM holds on to mainframe customers by refusing to license parts of its technology to other companies to build IBM-compatible machines.
Other US competitors have told the CCIA their customers have received letters from IBM, warning them of the legal risks of buying competitors' products.
Based on the allegations, the Department of Justice (DoJ) has sent requests for information to a number of US technology companies about practices in the mainframe market, according to the Financial Times.
IBM said it intends to co-operate with any inquiries from the DoJ, but believes it is fully entitled to enforce its intellectual property rights and protect investments made in its technologies.
European authorities are conducting a monopoly investigation into IBM after rival T3 Technologies filed a complaint in January.
T3 Technologies claims IBM has abused its monopoly by tying sales of its operating system to its mainframe hardware.
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