EU Competition Commissioner Margrethe Vestager said in a statement on Wednesday: "European consumers are increasingly shopping online. E-commerce has boosted retail competition and brought more choice and better prices. We need to ensure that large online platforms don't eliminate these benefits through anti-competitive behaviour.
"I have, therefore, decided to take a very close look at Amazon's business practices and its dual role as marketplace and retailer, to assess its compliance with EU competition rules.”
Vestager gave the first indications of such a probe in September last year when she announced that the EU had started taking a close look at Amazon's business practices.
The EC's Wednesday statement pointed out that Amazon's platform both sold products as a retailer and also allowed other retailers to sell products directly to consumers.
"When providing a marketplace for independent sellers, Amazon continuously collects data about the activity on its platform," the EC statement said.
"Based on the Commission's preliminary fact-finding, Amazon appears to use competitively sensitive information – about marketplace sellers, their products and transactions on the marketplace."
There is no legal deadline for the investigation to be concluded.