The European Union Commission has slapped a fine of 561 million euro ($733 million) on Microsoft for breaking the terms of an agreement to offer its users a choice of a default internet browser.

In 2009, Microsoft agreed to pay an 860 million euro fine and promised to give Windows users the option of choosing another browser rather than having Internet Explorer automatically installed.

But Microsoft failed to stick to the deal for some 15 million installations of Windows 7 in Europe from May 2011 until July 2012. The company admitted the failure last year, adding that it was a mistake.

The commission’s top regulator, Joaquin Almunia, said at a press conference in Brussels, Belgium on Wednesday that negotiated settlements are vital for enforcement to be carried out quickly. The penalty is a first for Brussels no company has ever failed to keep its end of a bargain with the EU authorities before.

However, he warned that the whole point would be undermined if companies then don't abide by the settlement terms. “They must do what they committed to do or face the consequences,” he said.  Almunia added that the large fine took into account the size and length of time the company violated the terms, as well as the need to defer other companies from going back on their promises to competition authorities.