Ireland should act to recover up to €13 billion from Apple in back taxes, the European Commission has ruled. After a three-year long investigation, it has concluded that the US firm’s tax benefits are illegal.

The commission concluded that Apple received “illegal state aid” from Ireland — essentially a sweetheart deal that allowed the computer maker to unfairly reduce its tax bill in a way not available to other companies, according to the report.

The Commission said this enabled it to pay substantially less tax than other businesses, in effect paying a corporate tax rate of 1%. Both Apple and the Irish government are likely to appeal against the Commission’s ruling.