The European Union is broadening its battle with Google, alleging that the technology giant rigs the global market for mobile apps by making sure its Android operating system gives preferential treatment to its own products.
EU antitrust commissioner Margrethe Vestager said "Google's behaviour denies consumers a wider choice of mobile apps and services and stands in the way of innovation".
Ms Vestager kicked off what is likely to be a protracted legal battle with a so-called Statement of Objections accusing Google of using its high market share in mobile operating software to force its own apps on customers.
The Android operating system is designed to automatically feature Google's search engine, maps, Gmail, YouTube video service and other products that give the company more opportunities to sell digital ads.
Device makers do not have to use Android as Google wants it to be, but European regulators are looking into complaints that the company penalises those that deviate from its Google-centric design.
The 28-nation EU also has other investigations against Google, with the biggest centring on its search services.
Four out of every five smartphones and tablets globally, and in the European market, use Android.
Google has stormed the market since it began eight years ago to give away its Android software for free to manufacturers to try to counter the runaway success of Apple's iPhone.
Now Android powers billions of mobile devices, largely because it does not cost phone and tablet makers anything to use the software.
"Dominant companies have a responsibility not to abuse their position," said Ms Vestager. "Google has abused its dominant position."
Google is based in Mountain View, California, and is owned by Alphabet.
Ms Vestager said the move in no way prejudges the outcome of its investigation.
"It is an interim step and not the end of the road," she said.
Google strongly denied the charges and said it was looking "forward to working with the European Commission to demonstrate that Android is good for competition and good for consumers".