Microsoft has once again come under fire for alleged anti-competitive behavior. This time Opera Software, maker of the cross-platform browser with the same name, has filed a complaint with the European Commission asking them to order Microsoft to either unbundle Internet Explorer from Windows or include an alternative browser on the operating system.

But Microsoft maintains that computer users are able to choose and set any browser as default, including Opera, and that PC makers can also pre-install any browser as a default on any Windows machine they sell.

This complaint is the first against Microsoft since the EU upheld the ruling in September that Microsoft had breached EU monopoly laws and was forced to unbundle its Media Player software from Windows and to divulge interoperability information to rivals.