BRUSSELS, Belgium — Microsoft is asking U.S. courts to compel Sun Microsystems, IBM, Oracle and Novell to hand over correspondence with European Union regulators on Microsoft's antitrust battle in Europe.

It filed papers Friday with federal courts in New York, Massachusetts and California, saying they could order U.S. citizens to provide evidence for use in foreign legal action.

Microsoft said it needs to see the documents to understand how an independent expert came to write reports critical of the company's efforts to comply with a 2004 EU antitrust order.

"We are now turning to the U.S. courts for assistance in obtaining relevant communications between our U.S. competitors and the commission," said Horacio Gutierrez, the company's associate general counsel in Europe.

Representatives from Sun, IBM and Oracle did not immediately return calls seeking comment. Novell spokesman Bruce Lowry said he couldn't immediately comment because the company hasn't seen the filing.

The dispute with the European Commission took a turn for the worse last December when the EU antitrust authority charged that Microsoft had not obeyed an order to provide competitors with the information needed to make servers work with Microsoft software.

Microsoft claims it worked strenuously to meet EU demands last autumn. It now says it thinks the commission colluded with its rivals and two outside experts ahead of the latest charges.

The EU said Thursday that it could not comment on Microsoft's allegations at this stage.

Microsoft alleged that regulators had "inappropriate contacts" with independent monitor Neil Barrett and the rival companies, calling into question the impartiality of a report in which Barrett said that technical documentation Microsoft had supplied needed a drastic overhaul to be workable.

The company also blasted the commission for holding back or failing to record information about these contacts.

Tyler Baker, head of antitrust litigation for the law firm Fenwick & West, said Microsoft's request for U.S. courts to intervene is unusual. He thinks U.S. courts would be reluctant to get involved with Europe's legal wrangling.

"To me, it show Microsoft's desperation, frankly, in dealing with the EU," he said.

Baker noted that it's not unusual for a regulator to have confidential dealings with competitors in an antitrust investigation. And he said Microsoft's efforts to try to force those contacts into the open could backfire by further souring relations with European regulators.

"This is really a last-gasp kind of strategic decision, because typically if you're dealing with a regulator that you are going to see again, you don't want to do something that's going to make them extremely unhappy," he said.

The EU has threatened to fine Microsoft $2.4 million a day, backdated to Dec. 15, for failing to provide usable information on the communications code at the heart of the dispute. It warned this week that the company was on course to be fined if it kept up its current conduct.

The EU levied a record $613 million fine against Microsoft in 2004. It also ordered the company to share code with rivals and offer a version of Windows without the Media Player software.

Microsoft is appealing the ruling, and the case will be heard next month by the European Court of First Instance, the EU's second-highest court.

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