Google may be facing an investigation from European regulators, the Financial Times reported, looking into whether it bolstered its Android mobile operating system by using unfair licensing and exclusivity agreements.

According to the report, the probe is “informal” and at “a preliminary stage,” but European antitrust authorities in Brussels have reportedly sent a questionnaire to companies that make Android devices as well as some mobile carriers.

In a statement, Google said, “Android is an open platform that fosters competition. Handset makers, carriers and consumers can decide how to use Android, including which applications they want to use.”

Microsoft and Nokia, which partner to produce some Windows Phone models, have complained in the past that Google’s platform gives it an unfair advantage in mobile search.

Google has previously faced questions about its desktop search practices from both U.S. and European regulators. As The Washington Post reported, a Federal Trade Commission probe ended in January and only demanded modest concessions from the tech giant over allegations that it was using its search engine to unfairly promote its own products.

European regulators, as The Post reported, demanded a little more from the company, ruling in April that it would have to make design and advertising changes to its Web search to denote its products more clearly.