EU regulators accused Apple on Friday of distorting competition in the music streaming market, siding with Spotify in a case that could lead to a hefty fine and changes in the iPhone maker’s lucrative business practices.

The preliminary findings are the first time Brussels has levelled anti-competitive charges against Apple, although the two sides have had bruising clashes in the past, most notably a multibillion-dollar tax dispute involving Ireland.

Apple, Spotify and other parties can now respond. If the case is pursued, the EU could demand concessions and potentially impose a fine of up to 10% of Apple’s global turnover – as much as $27 billion, although it rarely levies the maximum penalty.