European Union antitrust regulators have opened an investigation into whether Microsoft blocked computer makers from installing rival web browsers on the forthcoming Windows 8 operating system, following complaints from several companies.
EU competition watchdog spokesman Antoine Colombani said the investigation would also focus on allegations Microsoft allowed only its own Internet Explorer browser to be installed on devices running the lower-powered ARM version of Windows 8.
Colombani declined to identify the companies which made the allegations. Microsoft made no comment.
Windows 8 is expected to ship in late October.
The allegations flow on from an existing investigation into whether Microsoft failed to abide by a 2009 agreement that would provide consumers a choice of web browsers as part of the operating system setup process.
The company said a "technical error" prevented the option being display in the first service pack to Windows 7, released in February 2011 and affecting an estimated 28 million people in Europe.
Microsoft could be fined as much as ten per cent of its annual turnover, or $US7.4 billion, for not providing consumers the option to chose a different default browser than Internet Explorer.
The EU watchdog is also looking into allegations that Microsoft does not provide access to complete interfaces (APIs) for non-default browsers in Windows 8.