European competition authorities have broadened investigations into IBM's business practices in the mainframe market.
One area of investigation is looking into allegations that IBM refused to allow customers to run IBM's mainframe operating system on non-IBM hardware.
A second area of investigation is being brought on the commission's own initiative into whether IBM used anti-competitive tactics to keep competitors out of the mainframe maintenance services market.
IBM has promised to co-operate with the European Commission's investigations, but said there was no truth in the claims, according to the Financial Times.
IBM is entitled to enforce its intellectual property rights and protect the investments made in technologies, the company said.
Analysts estimate that as much as 20% of IBM's revenues and 40% of its operating profits still come from hardware, software and services related to mainframes.
IBM joins Microsoft, Intel and Google in the ranks of big US technology companies to be investigated by the EC for anti-competitive behaviour.