Now Meglena Kuneva, Bulgarian commissioner for the European Union, has weighed into the debate.

"Do you find it proper that a music CD can be played on all trademarks of players, but the music sold in iTunes can be played only on an iPod?" Kuneva told the German Focus magazine.

"I find it quite improper and I will do my best to change it."

Before you write off this attack as a simple rant by an unimportant minor commissioner from Bulgaria, it's important to realise that her role within the EU is to protect the rights of European consumers.

She's currently working on a consultation document that will outline the future laws on consumer rights across Europe.

So when she says she finds it "quite improper" it's time for Steve Jobs to sit up and take notice.

Apple could also still face separate legal action from Norway, which is not a member of the EU, after the government criticised iTunes' monopoly in January.

The Norwegians have set a deadline of October 2007 for Apple to open its digital rights management system up to other companies.