Google has been fined a record €4.34 billion by the European Commission (EC).
The EC said the firm had used the Android mobile operating system to illegally "cement its dominant position" in search.
Competition Commissioner Margrethe Vestager named three ways in which Google has allegedly acted illegally.
Firstly, by requiring Android handset and tablet manufacturers to pre-install the Google Search app and its own web browser Chrome as a condition for allowing them to offer access to its Play app store.
Secondly, by making payments to large manufacturers and mobile network operators that agreed to exclusively pre-install the Google Search app on their devices.
Thirdly, by preventing manufacturers from selling any smart devices powered by alternative versions of Android, by threatening to refuse them permission to pre-install its apps.
Google’s parent firm, Alphabet, has been given 90 days to change its business practices or face further penalties of up to 5 per cent of its average global daily turnover.
While the company has said it plans to appeal, it could easily afford the fine if required - its cash reserves totalled nearly €88.6bn at the end of March.