The European Commission’s antitrust enforcers are investigating Google’s app store rules, according to two people close to the matter.

Google's rivals have received confidential questionnaires from Brussels, probing billing terms and developer fees for the U.S. tech giant’s Play Store, the two people, who spoke on condition of anonymity, said.

An investigation in the Netherlands into Google’s Play Store rules will likely be closed to make way for the EU examination, the people added, as concerns of anticompetitive conduct will need to be examined on an EU-wide scale. The United Kingdom’s competition watchdog has also an open investigation into Google Play Store.

Developer fees for access to the Google Play Store can be as high as 30 percent, and developers have previously not been allowed to use alternative billing systems to collect payment from users.

The European Commission declined to comment.

A Google spokesperson said that the company had been discussing “a number of things” with the Commission, including recent changes to make terms and conditions on the Play Store fairer and to appease allegations from developers of unfair conduct.

In late July, the company said it would allow certain app developers to use alternative billing systems in the Play Store when collecting payments from users in Europe, and that it would reduce developer fees. The move was pitched by Google as a first step to comply with the bloc’s recently adopted landmark rules for the digital economy, the Digital Markets Act. The rules broadly set out a series of prohibitions and obligations for some of the world’s largest tech players, including Google, Meta, Amazon, Apple and Microsoft.

But some in the European Commission set to work on enforcement of the new regulation fear that Google’s recent moves “may not be sufficient” to remain in line with the rules, one person said.

The DMA is on course to be written into the EU rulebook this October, and tech firms under its scope will be brought into compliance in early 2024.