The move marks the latest example of Microsoft turning on rivals that have provided legal and political support to antitrust prosecutors.
Last week, Microsoft subpoenaed information that was posted on employee bulletin boards at Netscape. Yesterday, the software giant used a letter penned by Netscape's lawyer as evidence to support its position in the case.
One subpoena, sent to Netscape last week, seeks information about meetings Netscape held with key business partners. "We plan to show that companies throughout the software industry work collaboratively every day to compete against other companies," Microsoft spokesman Mark Murray said. "We plan to show that competitors are doing everything the government accuses Microsoft of doing, and then some."
Sun spokeswoman Lisa Poulson said it would be "quite a burden for Microsoft to prove" the allegations, but said the company is complying with the subpoenas. Netscape had no comment on the subpoenas.
The subpoena seeks details relating to Netscape's dealings with Sun, Apple Computer, Oracle, and other companies concerning numerous topics, including projects related to a "Global Unix" operating system, Java initiatives, and a Web browser written in Java.
Microsoft sent similar subpoenas to Sun, IBM, Novell, and Oracle, according to Murray, who provided CNET News.com with a copy of the Netscape subpoena. He said attorneys made the demands in response to a brief the Justice Department and 20 states filed last week.
In the filing, antitrust regulators introduced evidence concerning dealings with Apple, Intel, and RealNetworks that allegedly show Microsoft engaged in a "pattern of predatory conduct" concerning Sun's Java programming language, multimedia programs, and other Internet software.
Microsoft denies any wrongdoing and said the evidence it is seeking in last week's subpoenas will refute government claims.