LONDON — Amazon faces a widening inquiry in Europe over whether it unfairly uses data collected from third-party sellers who rely on its platform, the latest move by regulators around the world to curb the growing power of big technology companies.

The European Union’s top antitrust regulator said on Wednesday that it had opened a formal antitrust investigation into whether Amazon was using the third-party data to promote its own products at the expense of other retailers. A day earlier, representatives of Amazon, Apple, Facebook and Google were sharply criticized by lawmakers in Washington over the companies’ market dominance.

The announcement, by the European Commission, the bloc’s executive branch, is an incremental step in an inquiry into Amazon’s business practices that was described as “preliminary” in September. There is no hard deadline for the investigation to be completed, and it could last for years.

Regulators said they were examining whether Amazon was hurting competition by abusing its dual role as a retailer that sells its own goods and a marketplace where other merchants sell products.