Brussels has accused Amazon of breaching competition rules, alleging it abused its dominant position to gain an unfair advantage over smaller retailers on its platform.
Amazon rejected the claims and said no-one had done more to help small businesses over the last two decades.
Margrethe Vestager, the EU Commissioner for Competition, said the case pertained to "big data".
"We do not take issue with the success of Amazon or its size. Our concern is very specific business conduct, which appears to distort genuine competition," she said.
She argued that Amazon's dual role — as a platform and a retailer on that platform — means it not only competes with other companies but that is it privy to sensitive data about its competitors' performances from what they sell, at what price they sell, and what customers think of the products which then allows it to tailor its own offering.
'No-one supports small businesses better than Amazon'
"Our investigation shows that Amazon is able to aggregate …