District Court Judge Mark Wolf in Boston rejected Microsoft's attempts to subpoena sensitive information from Novell, which provided information to the European Commission for use in an antitrust case against the Redmond, Wash., firm.
"Enforcing Microsoft's...subpoena to Novell would circumvent and undermine the law of the European Community concerning how a litigant may obtain third-party documents," the judge said in a harshly-worded 12-page decision issued Monday.
The ruling was made available by lawyers in Brussels who oppose Microsoft.
A European Commission hearing officer, Karen Williams, had rejected Microsoft's request for a number of documents, ruling they were confidential. So Microsoft got U.S. courts to issue subpoenas, which were challenged by the target companies.
In March, a U.S. District Court in California quashed a similar attempt by Microsoft to force Sun Microsystems and Oracle to provide documents.
A judge in New York is considering a request against IBM.
Microsoft said it wanted the information to help it fight possible fines of up to 2 million euros a day, imposed for failing to carry out sanctions imposed by the Commission in 2004 for violating antitrust laws.
Next week, Microsoft goes before the European Union's second highest court, the Court of First Instance in Luxembourg, in a challenge to the Commission's underlying 2004 decision.
The European Commission question wound up in a United States court under a special section of American law designed to help foreign tribunals.
Wolf wrote that at first he had been leaning toward Microsoft.
But he said Microsoft "erroneously, repeatedly" told him the European Commission lacked authority to obtain certain documents from Novell and make them available to Microsoft.
As well, Wolf noted, the European Commission itself filed two memoranda with the judge opposing Microsoft's attempts.
"Microsoft's subpoena is a thinly veiled attempt to circumvent the procedures for and limitations on proof-gathering established by the laws of the European Community," the Commission told Judge Wolf, who quoted its words in his decision.
The Commission found in 2004 that Microsoft used its dominance of PC operating systems to compete unfairly against rivals.
The Commission fined Microsoft nearly half a billion euros and ordered it to provide rivals with protocols making it easier for them to build software that runs as smoothly on Windows as Microsoft's own server software.