The EU could hit Microsoft with another round of fines after the software giant failed to give Windows users a choice of browsers.
Sources told Bloomberg that the EU is readying a new complaint over the omission.
Microsoft had agreed with the EU in 2009 to offer PC buyers a choice of browsers, and - as recently as December - assured regulators that it was in compliance with the settlement.
Under the terms of the agreement, customers in the EU that bought PCs were given a selection of 12 popular browsers to install in addition to, or instead of, Internet Explorer.
The EU launched an investigation in July when it was discovered that the company had not offered around 28 million PCs running Windows 7 Service Pack 1 a choice of browsers.
Since February this year, that figure represents around 10 per cent of the user base that should have had the choice of browsers. Microsoft said it discovered the problem several months after it had happened.
The firm said the fault had been caused by a technical glitch and was not deliberate. It volunteered to extend the agreement it had with EU regulators until March 2016.
Sources told Bloomberg there was no set timing for the European Commission to send the statement of objections.
This statement lists alleged competition rules violations and is a precursor to a possible fine, which would be limited to 10 per cent of the firm's yearly revenues.
Any fines may take into account previous offences, EU Competition Commissioner Joaquin Almunia said in July.
Microsoft has already been fined 1.68 billion euros (1.34 billion) in EU antitrust probes, including an 899 million euro (720 million) fine after failing to obey an order to share data with rival companies.
