The EU has launched a probe into what Apple's online music store iTunes charges users across Europe, accusing it of restricting customer choice.
Brussels believes agreements between Apple and record companies violate EU laws by preventing users in one country buying music from a site elsewhere.
The move follows a complaint by UK body Which? that British users have to pay more to download songs than others.
Apple said it wanted to offer a single European service but faced obstacles.
Different pricing
The Commission's move is unrelated to an agreement, announced on Monday, between iTunes and EMI to make the latter's music available online without piracy protection.
Brussels has written to iTunes and a number of unnamed record companies to notify them of their objections to the way music is sold, the first step in formal proceedings.
"Consumers can only buy music from the iTunes online stores in their country of residence and are therefore restricted in their choice of where to buy music," said EU competition spokesman Jonathan Todd.
Research by Which? in 2005 found that UK users paid 79p (1.16 euros) to download a song compared with 66p (99 euro cents) in France and Germany.
Apple said it had always wanted to offer a fully pan-European service but was restricted by the demands of its music partners.
"We were advised by the music labels and publishers that there were certain legal limits to the rights they could grant us," it said in a statement.
The companies targeted by Brussels have two months in which to respond to the charges.
- BBC
It's about time.
We've being paying too much on too many things in the UK for far too long.