The European Commission on Tuesday opened proceedings against Microsoft to investigate claims that the US firm had failed to meet its 2009 commitment to offer users a choice screen enabling them to easily select web browsers other than Microsoft's Internet Explorer.
"On the basis of information it has received, the Commission believes that Microsoft may have failed to roll out the choice screen with Windows 7 Service Pack 1, which was released in February 2011," the EU's executive body said in a statement.
"This is despite the fact that, in December 2011, Microsoft indicated in its annual compliance report to the Commission that it was in compliance with its commitments. From February 2011 until today, millions of Windows users in the EU may have not seen the choice screen. Microsoft has recently acknowledged that the choice screen was not displayed during that period."
Competition Commissioner Joaquín Almunia said Microsoft would face a fine if the investigation confirmed the accusation.
He said Microsoft did not appear to be contesting the facts, and that this would be the first time such a legally binding agreement had not been complied with.
"Needless to say, we take compliance with our decision very seriously," he said. "If the infringement is confirmed, there will be sanctions."
Microsoft said on Tuesday a technical glitch had prevented it from offering users the choice of browsers it had promised and that it was taking steps to fix the problem.
"Due to a technical error, we missed delivering the BCS (browser choice screen) software to PCs that came with the service pack 1 update to Windows 7," Microsoft said in a statement.
"While we have taken immediate steps to remedy this problem, we deeply regret that this error occurred and we apologize for it."