Apple’s legal representatives slammed a 2016 European Commission (EC) decision to charge the company €13 billion in back taxes as defying common sense, at the opening of its long-awaited appeal hearing, Reuters reported.

The iPhone manufacturer was charged the mammoth sum for receiving what the EC said was illegal tax benefits in the Republic of Ireland between 2003 and 2014.

Opening the appeal, Apple argued the original decision had been “fundamentally flawed”.

In its original judgement, the EC said Ireland had allowed Apple to pay substantially less tax than other businesses, contravening European Union state aid rules. Ireland was ordered to recoup the funds, though the country also contested the validity of the decision.

Apple paid the fee including interest in 2018, though the €14.3 billion went into escrow pending a final court decision.

In addition to the manufacturer and the EC, the appeal at the EU’s General Court in Luxembourg will hear evidence from lawyers representing Ireland and a number of other EU countries.

Evidence will be presented over the next two days with a decision expected within the next two months. A further appeal would likely then be heard by the European Court of Justice.