BRUSSELS — While the U.S. Congress talks about reining in big tech companies, Europe is taking action.

The European Union said Wednesday it is investigating whether Amazon uses data from independent retailers to gain an unfair advantage, a decision that could lead to changes in how the internet’s biggest marketplace works.

The move echoes similar antitrust actions against Google and Microsoft that have led to billions in fines. It also contrasts with U.S. lawmakers’ slower approach to the issue, as they start discussing how to curb the growing power of the tech industry’s titans. A Tuesday hearing in Washington looked into whether the companies’ business practices run afoul of century-old laws originally designed to combat railroad and oil monopolies. Any U.S. action is still a long time away.

The EU’s antitrust chief, Margrethe Vestager, said she’s taking a “very close look” at Amazon’s dual role as marketplace and retailer.

In addition to selling its own products, Amazon allows third-party retailers to sell their goods through its site. Last year, more than half of the items sold on Amazon worldwide were from third-party sellers.

In doing so, Amazon collects data about activity on its platform that, the EU says, it might be able to use to favor its own products for sale. In particular, the EU will look at how Amazon determines which trader is selected as the default seller of an item that a customer wants to buy.

The EU opened a preliminary probe into the issue last year, and Vestager said it has shown that “Amazon appears to use competitively sensitive information — about marketplace sellers, their products and transactions on the marketplace.”

The investigation could lead to fines and eventually cause Amazon to change the way it works. Previous EU antitrust cases have resulted in such change, though it is unclear how big their ultimate impact has been in addressing the EU’s concerns. For example, Google had to tweak the display of search results, which the EU had said favored Google goods and services.

Amazon said it “will cooperate fully with the European Commission and continue working hard to support businesses of all sizes and help them grow.”

During Tuesday’s hearing before a House panel, Amazon associate general counsel Nate Sutton said Amazon has an incentive to keep third-party sellers strong because they make up nearly 60% of unit sales for Amazon and are growing twice as fast as Amazon’s own retail operations.

Sutton insisted that Amazon uses data to serve customers. His remarks echoed executive Jeff Wilke’s insistence in June that no one inside Amazon shares seller data to create competing Amazon private-label products.