Jeff Chiu, Associated Press
Kirk Koenigbauer, Corporate Vice President of Microsoft Office Division, speaks at a Microsoft event in San Francisco, Monday, July 16, 2012. Microsoft unveiled a new version of its widely used, lucrative suite of word processing, spreadsheet and email programs Monday, one designed specifically with tablet computers and Internet-based storage in mind.

BRUSSELS — The European Union's executive body, the Commission, is to open an investigation into whether Microsoft has kept to the antitrust commitments it made in 2009, warning that penalties for non-compliance could be "severe".

EU Competition Commissioner Joaquin Almunia told reporters Tuesday that the indications are that Microsoft, the company behind the Windows operating system, has failed to provide customers with a screen from which they could chose different internet browsers other than just Microsoft's Internet Explorer.

Almunia says it appears that the "choice screen", promised by Microsoft following an antitrust case in 2009, has not been provided since February 2011 — with the introduction of Windows 7 Service Pack 1 — meaning 28 million customers may not have seen it.

Almunia said Microsoft does not appear to be contesting the facts. He also said this would be the first time such a legally binding agreement has 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."