Amazon.com Inc. faces a formal antitrust complaint from the European Union, which could pave the way for massive fines or changes to Amazon’s business model.

EU regulators will send out a so-called statement of objections in the coming weeks amid concerns the U.S. giant may be shortchanging smaller merchants who sell on its marketplace, according to a person familiar with the case who spoke on condition of anonymity.

The complaint is expected to lay out investigators’ evidence into Amazon’s potential misuse of merchants’ data on the online sales platform.

The world’s biggest online retailer is one of several tech platforms facing intense scrutiny from the EU’s powerful competition watchdog. Regulators are wrestling with how to act against online giants that may run a rigged game when they set the rules for a platform that also hosts their rivals.

EU officials have quizzed online merchants over the past year and a half to build a picture of how Amazon competes to win a “buy box” on the website that tells users whether they can purchase a product from Amazon or from a retailer using Amazon’s Marketplace.

As the operator of the platform, Amazon (AMZN) gathers data on hit products and user demand that can help it jump ahead of smaller sellers. It’s also increasingly pushing its own-brand products that are similar to bestsellers offered by others.

The Wall Street Journal earlier reported that the EU would send a statement of objections next week or the week after. Amazon declined to comment. The commission’s press office declined to comment beyond confirming that the investigation is ongoing.

EU antitrust probes haven’t always opened the way to more competition. Google’s smaller rivals complain that the company hasn’t had to cede much despite a decade of EU probes and $9 billion in penalties.

Regulators are looking for new antitrust powers that could order changes without fines and are seeking rules for so-called gatekeeper platforms that could curb the power of big tech.

Google (GOOGL), Facebook Inc. (FB) and Apple Inc. (AAPL) have also attracted fresh EU attention over how they might push users to their own services over competitors.