By picking on Apple, Brussels risks spreading fear - the very thing that drove voters in the UK to leave
State aid rules were originally designed to protect the internal EU market and avoid retaliation among member states. The US Treasury, which last week began a vocal fight-back, believes the European Commission is bending these rules to breaking point to target the earnings of American companies.
Under international tax regulations these are predominantly taxed in the US where value is generated, although US rules allow taxes to be deferred until profits are repatriated.
With a decision in the investigation into Ireland's tax arrangements with Apple expected this week, the stakes are high, with possible retaliatory measures against European companies and concerns it will take its toll on investment in Europe.