Google has been issued formal antitrust charges over claims that it abuses the dominant position of its Android operating system.
The European Commission sent a statement of objections to the tech firm, alleging that it has breached EU competition law.
Google is accused of placing onerous requirements on firms using Android and stifling competition.
[European competition commissioner] Ms Vestager said Google had harmed both competitors and consumers by placing requirements on mobile manufacturers and operators to preinstall some of its own products and, in some cases, set them as default or exclusive options on handsets.
In some cases, she said, this had been as a condition of Google's agreement to grant a licence for the use of some of its apps.
Android is open-source software, meaning competing operating systems can be built using its source code.
The commissioner alleged Google had barred manufacturers from selling devices using these operating systems.
She also said Google had given financial incentives to manufacturers and mobile network operators on condition they exclusively preinstalled Google Search on their devices.