It was a violation of Irish competition law, which as a part of the EU is harmonised with EU law. Seemingly the Irish officials were unaware of certain nuances, or at least were blithely ignorant.
It was not a violation of competition law either. The EU's basis for forcing Ireland's hand here is a novel redefinition of "state aid". Previously this part of the EU treaties had been understood to be talking about subsidies. The language contains a reference to the usage of "state's own resources" which is EU speak for government money. The goal was to stop the common practice of governments bailing out national champion firms.
But the EU can be relied upon to expansively re-interpret its powers after they have been agreed. It happens frequently. They have since decided that in Ireland's case, low tax rates are the same thing as direct subsidies. Obviously Ireland is not giving money to Apple, it's the other way around, but now "not enough" money is considered by the EU to be illegal.
This interpretation of the treaties was never raised previously and not surprisingly Ireland was very upset about it, as they'd been given assurances the EU would not interfere with their low corp tax regime. That's why Ireland is fighting it on Apple's side. It's not just about Apple. It's about the EU taking control of a policy that the Irish government thought they controlled.
That's not the case. Sorry. It certainly isn't that the EU redefined anything. These rules are quite clear.
What is less clear is the nuances of "just how" Apple was given favourable treatment.
It's very much in the fine details of Ireland's agreement with Apple, but what it boils down to is that Ireland gave an evaluation of Apple's tax liabilities tailored to Apple.
Even without this, Apple's tax liabilities would have been highly favourable but it is this "technical" matter that puts Apple & Ireland over the line, and is the basis of the 13bn figure, which is only a fraction of what Apple actually manages to avoid paying with their creative tax practices.
The best plea that Ireland can make in this regard is ignorance, but now that rules have been clarified the adjustments must be made.
I felt that Apple's whole response to this was highly disingenuous and inflammatory.
You should really discuss that with a tax lawyer. If the rules are so clear then why was Ireland taken by surprise and why did they fight it? The relevant section of the treaties are quite clear and readable. They simply would not be interpreted by any normal person in this way.
It is a power grab by the EU in an area that the treaties explicitly state the EU does not control. End of story.
edit: Also see below where I discuss the article in question, which is anything but clear
But the EU can be relied upon to expansively re-interpret its powers after they have been agreed. It happens frequently. They have since decided that in Ireland's case, low tax rates are the same thing as direct subsidies. Obviously Ireland is not giving money to Apple, it's the other way around, but now "not enough" money is considered by the EU to be illegal.
This interpretation of the treaties was never raised previously and not surprisingly Ireland was very upset about it, as they'd been given assurances the EU would not interfere with their low corp tax regime. That's why Ireland is fighting it on Apple's side. It's not just about Apple. It's about the EU taking control of a policy that the Irish government thought they controlled.