IBM is facing an antitrust inquiry from the US Department of Justice over its mainframe business.

US regulators have begun issuing formal requests for information related to a complaint filed against IBM in September, according to the Computer and Communications Industry Association (CCIA), the trade group that filed the complaint.

CCIA's complaint against IBM alleges that the company has refused to issue licences for IBM's mainframe OS to competitors, as required in a series of actions the DoJ took against IBM dating back to the 1970s and earlier. In some cases, IBM has yanked the OS licence from customers trying to switch from IBM mainframe hardware to a competitor's, said Ed Black, CCIA's president.

The DoJ abandoned a long-standing antitrust consent decree with IBM in 2001.

Several large and small companies would like to compete with IBM in the mainframe market, particularly in software and services for mainframes, but IBM's actions have allowed the company to maintain a monopoly, Black said.

"It's a really big case," added Heather Greenfield, a CCIA spokeswoman. "There are tons of companies cheering that aren't willing to be quite so public because they have to deal with IBM in other ways."

The DOJ will not comment on the complaint, a DoJ spokeswoman said.

IBM believes there is no merit to antitrust claims brought by competitor T3 Technologies, said Tim Breuer, director of external relations for the IBM Systems and Technology Group. The DoJ has apparently asked T3 for documents related to its lawsuit, Breuer said. IBM intends to cooperate with any inquires from the DoJ, he added.

Last week, a US district court in New York dismissed a lawsuit brought by mainframe vendor T3, Breuer noted.

T3, partly owned by Microsoft, had accused IBM of yanking its IBM reseller agreement when T3 refused to stop selling technology that allowed customers to end older versions of IBM's mainframe operating systems on Intel-based servers.

The T3 dispute with IBM is part of CCIA's complaint filed with the DoJ, as well as part of an antitrust investigation against IBM launched by the European Union in mid-2008.

"We continue to believe there is no merit to T3's claims, and that IBM is fully entitled to enforce our intellectual property rights and protect the investments that we have made in our technologies," Breuer said.

Part of CCIA's complaint stems from the tech company's treatment of former competitor Platform Solutions. IBM had little competition in the mainframe market before early this decade, when Platform Solutions began work on servers that could mimic the behaviour of more expensive IBM mainframes, CCIA said.

Based on past mainframe agreements between IBM and the DoJ, Platform Solutions requested copies of IBM's OS and technical information under a licensing agreement. IBM declined and prohibited customers from transferring IBM software licences to Platform Solutions machines, said CCIA, which has members that are potential competitors of IBM.

In 2006, IBM sued Platform Solutions over licences the smaller company had purchased from Amdahl, a division of former mainframe competitor Fujitsu. IBM's lawsuit alleged that the licences infringed its intellectual property. Platform Solutions filed a countersuit. In 2008, IBM purchased Platform Solutions, putting an end to the legal wrangling.

IBM also refused to licence its mainframe OSes to users of the Hercules open source mainframe project trying to run mainframe software on non-IBM hardware, CCIA said.

But the complaint goes "way beyond" the Platform Solutions, T3 and Hercules cases, Black said. Many mainframe customers would like to find cheaper alternatives, but IBM has prevented them from doing so, he said.

"There's a number of things they have done to numerous companies," he said. "In a time of economic troubles, government deficits and corporate problems, there's a lot of customers that [would find] a choice and lower costs really desirable."