Microsoft (Nasdaq: MSFT) was fined $731 million by European Union regulators for violating the terms of a settlement to give users a choice of web browsers aside from its Internet Explorer.

Wednesday’s fine – about 1 percent of the company’s 2012 revenues – brings to some $2.5 billion the penalties faced by Microsoft in its EU antitrust clashes over the past decade, including a some $1 billion fine for failing to obey an order to share data with competitors.

The commission’s top regulator, Joaquin Almunia, said negotiated settlements are vital for enforcement, and this was the first time a company had failed to keep its word.

“A failure to comply is a very serious infringement that must be sanctioned accordingly,” Almunia said in an e-mailed statement.

The world’s largest software maker agreed in 2009 to offer access to rival browsers as a part of a settlement to repair its relationship with the bloc’s regulators. The company said last July it only learned that month that it didn’t offer its browser choice software to some 28 million computers running Windows 7 Service Pack 1, or 10 percent of the computers that should have received it.

The company acknowledged the failure and said it was a mistake.

The Redmond, Washington-based company told regulators in December 2011 that it was complying with its commitment to display a browser-choice screen to users of its Windows operating system.