Updated from 8:21 a.m. EDT

European regulators hit Microsoft ( MSFT) with another stiff fine Wednesday, saying it has failed to comply with its 2004 antitrust settlement.

The European Union Commission fined Microsoft $357 million and warned of additional penalties of nearly $4 million a day starting next month if the company remains out of compliance. Regulators say Microsoft hasn't made good on a pledge to provide other software makers source code for its Windows operating system.

Shares of Microsoft were recently off 27 cents, or 1.2%, to $22.83.

In March 2004, the EU regulators fined Microsoft more than $500 million and imposed the source-code requirement after finding the software company had abused its dominant position in the software industry to hamper competition.

Microsoft said it would appeal the fine, which it said is unfair and excessive. The company said it didn't receive a clear definition of what regulators wanted until April and, with 300 employees working on compliance since then, has met "nearly all those requirements" in the three months since.

"The record will show that Microsoft has acted in good faith to comply with the commission's decision," the company said. "We delivered thousands of pages of technical documents from December 2004 onward. When it became clear there were disagreements over the technical documentation requirements, we pressed for greater clarity, we delivered revisions promptly, we offered unlimited technical assistance, and we even made our source code available to competitors in an effort to resolve the impasse."

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