A senior adviser to one of the EU’s highest courts delivered an unexpected decision Thursday that could see Apple bite the dust in a yearslong legal wrangle with the European Commission involving a €13 billion tax bill.

In his opinion, the EU Court of Justice Advocate-General Giovanni Pitruzzella stated that an EU tribunal made legal errors when it ruled in favor of Apple regarding a €13 billion ($14 billion) tax order and should review the case again. The opinion is seen as a potential setback for the iPhone maker. The EU’s top judges heed the advocate-general’s advice in most cases.