Last year the European Commission opened an in-depth investigation into Amazon’s Luxembourg tax arrangements, which may be illegal. Amazon funnels its European revenues through a complex transfer pricing set-up in the duchy, effectively resulting in an especially low tax rate (see also: Skype). This nets Luxembourg a lot for a country that size, but countries in the rest of the EU get way less than they should. On Friday the Commission published a public version (PDF) of its decision to launch the investigation, detailing why it thinks the 2003 arrangement represented a special deal for the company, making it illegal state aid. If the investigation finds as much, Amazon may have to pay a whole bunch of back taxes.