An Apple logo is seen on the outside of an Apple store in San Francisco, California. AFP

Apple went on the offensive against Brussels in an EU court on Tuesday, fighting the European Commission's landmark order that the iPhone-maker reimburse Ireland 13 billion euros ($14 billion) in back taxes.

The EU's tax demand, made three years ago, "defies reality and common sense," Apple's lawyer Daniel Beard told the EU's lower General Court.

The commission's "conclusion... is wrong," he added at the start of two days of hearings.

This file photo shows a view of buildings on The Apple campus in Cork, southern Ireland. AFP

Lawyers for the world's biggest company faced EU officials in the Luxembourg court, challenging a decision that CEO Tim Cook slammed at the time as "total political crap" with no basis in law.

Ireland, which is similarly appealing the decision, lashed out at the EU's "astonishing" interpretation of tax law.

"The Commission decision simply ignores Irish laws," Ireland's representative Maurice Collins told judges.

The commission's historic decision was delivered in August 2016 by Competition Commissioner Margrethe Vestager, a shock decision that put Europe at the forefront of an emerging effort to rein in the power of America's largest technological companies.

The EU accuses Apple of parking untaxed revenue earned in Europe, Africa, the Middle East and India in Ireland, which has become a European hub for US-based big tech.

This privilege allegedly gave Apple an advantage over other companies, allowing it to avoid Irish taxes between 2003 and 2014 of around 13 billion euros which, according to Brussels, constituted illegal "state aid" by Ireland.

An EU lawyer pushed back at Apple and Ireland's arguments, insisting that the iPhone-maker was on the hook to pay taxes in Ireland.

The judges are not expected to hand down their decision before 2020. Any appeal would then go the EU's highest court, the European Court of Justice, for a final ruling that could land as late as 2021.

Agence France-Presse