European Union regulators have laid down fresh claims that Microsoft is again in breach of its anti-trust laws.
The complaint is related to Internet Explorer being bundled with all new Windows installations.
Microsoft lost a similar case in 2004 and was forced to sell Windows versions without Windows Media Player.
This has potential repercussions across the market. Apple currently bundles Safari with every copy of Mac OS X, while most Linux distributions are bundled with Firefox.
“Microsoft’s tying of Internet Explorer to the Windows operating system harms competition between web browsers, undermines product innovation and ultimately reduces consumer choice” said a spokesman for the European Union.
Any final decision on the matter is likely to be years away.