Does Jeff Bezos dream of being chased through a dark forest by Margrethe Vestager? He should. This year alone, the European Union’s competition commissioner stalled Apple’s Shazam acquisition (it’s cleared now), fined Qualcomm $1.23 billion, and hit Google with a $5 billion fine for Android anti-trust violations.

In 2017, Vestager ordered Amazon to pay Luxembourg €250 million for receiving illegal back taxes. Now she has the online retailer in her sights again.

On Wednesday (Sept. 19), Vestager announced that she had started sending questionnaires to merchants who sell on Amazon, a first step toward ascertaining how the company uses the data it collects from those merchants. Specifically, she will be trying to find out if Amazon uses data from its third-party sellers to give itself an unfair advantage when competing against them in selling its own products.

“These are very early days and we haven’t formally opened a case,” Vestager said. “We are trying to make sure that we get the full picture… because this is also what a lot of people are talking about right now.”

Amazon’s dual role as the world’s biggest online platform for third-party sellers and a retailer itself merits examination, according to the antitrust chief.

Should she find evidence of anti-trust behavior, the commissioner has the power to fine companies up to 10% of their global turnover. Based on Amazon’s 2017 net sales, that would be in the neighborhood of $17 billion.