European competition watchdogs have accused Google of breaking EU law over commercial practices relating to its Android operating system.
The European Commission has written to the internet search engine giant, owned by Alphabet Inc (NASDAQ:GOOG), accusing it of slapping cumbersome conditions on companies using Android.
Brussels claimed the "onerous requirements" breach the EU’s regulations by stifling competition.
Google has 12 weeks to respond, and, if found guilty, faces a fine and may be told to change its practices.
The EU claimed Google had harmed both competitors and consumers by forcing mobile manufacturers and operators to pre-fit some of its own products and sometimes make them default or exclusive options on handsets.
In some cases, this was in return for Google agreeing to grant a licence to use some of its apps.
European competition commissioner Margrethe Vestager said: “A competitive mobile internet sector is increasingly important for consumers and businesses in Europe.
"Based on our investigation thus far, we believe Google's behaviour denies consumers a wider choice of mobile apps and services and stands in the way of innovation by other players, in breach of EU antitrust rules.
"These rules apply to all companies active in Europe."
Google said Android was "good for competition and good for consumers".
Kent Walker, Google's senior vice president and general counsel, said: "Android has helped foster a remarkable and, importantly, sustainable ecosystem, based on open-source software and open innovation.
"We look forward to working with the European Commission."
Shares in Alphabet fell 0.4% to US$751 in early New York trading.