Microsoft, Hewlett-Packard, Sun Microsystems and BayStar Capital must hand over details of their involvement with SCO, according to the subpoenas, which were filed in US District Court in Utah, where the case between IBM and SCO is being heard.
IBM, meanwhile, is building its defences against the charge that it included SCO's Unix code in its version of Linux.
The subpoenas demand that Microsoft, HP, Sun and BayStar hand over a range of information, including details of their dealings with SCO, by 7 March. They will also have to appear in court later in March to give depositions.
Groklaw, a legal Web site that had been following the case closely, believes that the subpoenas could help bring important information about the case to light.
"I begin to think that every question we've had, we will finally get to know the answer," wrote Groklaw's Pamela Jones, who published the subpoenas on the Groklaw site.
Back in March 2003, SCO filed a lawsuit alleging that IBM had included code from Unix in its contribution to Linux, which SCO claimed was a violation of its intellectual property. However, Novell then claimed that it, rather than SCO, owned the copyright on Unix, which prompted another lawsuit from SCO. In August 2003, IBM countersued SCO.
The subpoenas filed on Tuesday are part of the discovery phase of the case, during which IBM can gather evidence in its defence.
Microsoft's subpoena runs to 13 separate demands. They include handing over details of agreements relating to any Unix product involving Microsoft and SCO, and all communications between the two companies. In early 2003, Microsoft started paying SCO what eventually grew to US$16.6 million for a Unix licence, according to regulatory filings. Only longtime Unix fan Sun previously paid close to that, with a US$9.3 million licence deal. Microsoft provided a second, though indirect, boost in August or September of 2003, when it referred SCO to BayStar, a fund that arranged a US$50 million investment.
Sun itself must reveal details of any agreements or licenses between it and SCO for the Unix source code, any documents referring to the open-sourcing of any of its Unix products, as well as Sun's involvement in the development of Linux.
HP has been ordered to give the court details of "agreements relating to any Unix software product involving HP and AT&T, USL (Unix System Laboratories), Novell, Santa Cruz (Operation) and SCO," as well as details of any royalties HP pays for Unix and the origin of any Unix source code publicly disclosed or open-sourced by HP.
It also forces HP to disclose any communications it has had with SCO since June 28, 2002.
BayStar must hand over details of its communications, agreements and investments in SCO. It must also reveal communications between it and Microsoft regarding SCO, IBM and the ongoing court case.
After its October 2003 investment, BayStar began attempting to force changes at SCO.
ZDNet UK's Graeme Wearden reported from London. For more coverage from ZDNet UK, click here.