The European Union is investigating yet another U.S tech company on antitrust grounds. Margrethe Vestager, the E.U.’s main trust-buster, announced Wednesday that regulators are looking into Amazon’s use of data from its smaller third-party sellers, Reuters reported.

The E.U.’s primary concern with Amazon is that the third-party merchants whose products are hosted on the site are also technically Amazon competitors. However, by going through Amazon’s system to sell their wares, they are giving data to Amazon that the e-commerce giant could use in its competition with said retailers.

In a press conference, Vestager emphasized that this is a preliminary step and there is not yet a formal case against Amazon.

“We are gathering information on the issue and we have sent quite a number of questionnaires to market participants in order to understand this issue in full,” Vestager said.

The news comes on the same week in which Amazon launched a feature meant to support third-party sellers. The new Storefronts page on Amazon gives customers a way to shop exclusively from the “small and medium” businesses that make up a significant portion of the site’s product offerings. In fact, Amazon claims half of everything on Amazon comes from these sellers.

The E.U. generally fights harder antitrust battles than the U.S. government. Vestager’s regulators have come down on big tech companies, in particular, having levied a $5 billion fine against Google earlier this year. The commission charged Google with asserting its dominance in the mobile phone market by making hardware companies install pre-install Google apps on Android smartphones.

President Donald Trump later criticized the E.U. for its fine on Google, calling the California-based tech giants “one of our great companies.”

The E.U.’s investigation may not reach any significant conclusion, but it is the latest instance of someone with institutional power criticizing Amazon for its size and business practices.

Sen. Bernie Sanders of Vermont has also blasted the company recently for allegedly unsafe working conditions at its many fulfillment centers. The company firmly denied the allegations, but Sanders still  introduced corporate tax legislation, which was named after Bezos.