But it did a lot more than simply offer a low corporate tax rate. It set itself up as a kind of European tax haven, so that companies like Google, Facebook, Microsoft and others could, in effect, buy an Irish address to which they could transfer a great deal of their intellectual property and route profits accrued elsewhere through the Irish subsidiary. This is called transfer pricing. Companies could also take advantage of other loopholes in the Irish tax code to get their tax bill considerably lower than 12.5 percent.

As The New York Times reported in a groundbreaking article two years ago — and the Senate Permanent Subcommittee on Investigations confirmed last year — Apple takes advantage of every tax break Ireland offers. But according to the European Union’s competition commissioner, Joaquín Almunia, in a letter released this week, the company went a step further in its dealings with the Irish tax authorities.

In 1991, Apple essentially negotiated how much tax the company would pay. It did so after it had explicitly “mentioned by way of background information that Apple was now the largest employer in the Cork area with 1,000 direct employees and 500 persons engaged on a sub-contract basis,” again according to Almunia’s letter. Apple also acknowledged that it had “no scientific basis” for the amount of tax it was willing to pay. The deal was then “reverse engineered” so that Apple’s profits would wind up in the range that would yield the suggested taxes. (Apple now has 4,000 people working in its Cork manufacturing plant, the only Apple-owned factory in Europe; its tax deal with Ireland was reworked in 2007.)

With the recent outcry over corporate tax loopholes, the E.U. decided to take a closer look at some of its members’ tax dealings that had been flagged in the media. In addition to Apple and Ireland, it is looking at Fiat in Luxembourg and Starbucks in the Netherlands. And while the Apple case is far from over — indeed, both Apple and Ireland insist they did nothing wrong — Almunia, at least, has concluded that Apple’s tax deal with Ireland amounts to “state aid.” Under European Commission rules, countries are not allowed to subsidize companies in ways that give them advantages over others in the country.

Here then is one difference between what transpires in the U.S. and what transpires in Europe: The E.U. has rules intended to prevent nations from giving unjustified tax breaks to companies. “In Europe there is now a mechanism to prevent the most harmful abuses” of the tax code, said Matthew Gardner, the executive director of the Institute on Taxation and Economic Policy. It has taken a while — and required an outraged public to spur it on — but the E.U. finally seems intent on curbing excesses like Apple’s tax deal in Ireland.