The European Commission this morning took another step toward a possible fine against Microsoft and delivered a public warning to the company over a component of Windows 8, two days before the release of the new operating system.

Antitrust regulators say they have reached a preliminary finding that Microsoft failed to comply with its promises under a 2009 antitrust settlement, after a Windows update left out a “ballot” designed to make it easier for PC users to choose competitors to Microsoft’s Internet Explorer browser.

Microsoft has acknowledged the mistake and recently trimmed the bonuses of CEO Steve Ballmer and Windows president Steven Sinofsky, saying they were ultimately responsible for what happened.

The company said in a statement this morning, “We take this matter very seriously and moved quickly to address this problem as soon as we became aware of it. Although this was the result of a technical error, we take responsibility for what happened, and we have taken steps to strengthen our internal procedures to help ensure something like this cannot happen again. We sincerely apologize for this mistake and will continue to cooperate fully with the Commission.”

Regulators delivered the preliminary finding to Microsoft in a “statement of objections,” the latest step in a process that could lead to a significant fine against the company — as much as 10 percent of annual revenue, or $7 billion.

In a statement to the press, Joaquín Almunia, the European competition commissioner, also addressed the upcoming Windows 8 release. He said, “Based on our own monitoring, we have raised issues to Microsoft relating to Windows 8, which is to be released soon. If a user decides to set a rival browser as the default browser, there should not be unnecessary warning windows or confirmations by the user, and the Internet Explorer icon should also be unpinned from the Start screen. We expect Microsoft to address these issues.”

Update: Here’s what Microsoft says on the Windows 8 issue: “After discussions with the Commission, we are changing some aspects of the way the Browser Choice Screen works on Windows 8 and will have those changes implemented when Windows 8 launches later this week.”

The New York Times cites legal experts who say the commission is using the case, in part, to send a message to Google as the search giant tries to resolve its own antitrust issues in Europe.

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