It's not a new rule.

They just found that Ireland's tax rules from 1991 and 2007 are illegal tax benefits according to the preexisting rule.

Just because they took so long apply existing law doesn't make it retroactive.

While that sounds true, the EU approved Ireland's 1% tax rate.

This is a retroactive ruling. This is playing favorites, the opposite game.

An approval doesn't mean it's legal. When they finally looked into it they found it's violating existing laws.

Same with the data contracts with the US, Safe Harbor, Privacy Shield etc. All approved, all later on found a violation of EU law.

That's not retroactive just slow.

Even if it was retroactive, which it is not, being punished for premeditated tax avoidance can hardly be called unpredictable.

The central difference of opinion is of course whether outright gaming the system is acceptable regardless of the written rules being followed to the letter.