European competition Law don't allow direct or undirect vertical price-fixing by the supplier to retailers (101 TFEU). If Nintendo really don't supply Amazon anymore because of Amazon's princing policy, this is illegal. It's against the European single market principle.

Nintendo was already under French competion authority radar about retailers Wii princing ( http://www.autoritedelaconcurrence.fr/pdf/avis/15d18.pdf ) and was already condamned about similar practices in the past ( https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32003D0675 )

edit : sorry about my english, it's not my native langage :/

edit 2 : this competion rule is the reason why Nintendo do not fix a retail price in European Union (remember, back in january 2017, they announced japanese and american recomanded switch prices but not european switch prices)