Officials of the 28-nation
The EU's antitrust chief, Margrethe Vestager, also opened a separate probe into whether Google abused its widely used Android mobile operating system to hinder the development of rival software and products.
Google disputed the allegations and will be allowed to mount its defense. That process, along with possible court appeals if the company is found to be in violation of antitrust rules, could drag on for years.
If Google fails to overturn the EU's allegations, there is speculation that the Mountain View, Calif., concern could face fines in the billions of dollars.
The EU's prior high-profile antitrust case involved Microsoft, which ended up paying hefty fines and being forced to alter its business practices in Europe.
Officials levied a combined $2.1 billion in fines against the software giant after investigations that began in the late 1990s.
Officials at the European Commission, the EU's antitrust regulator, alleged among other things that Microsoft abused its dominance in personal-computer operating software to limit competition.
Microsoft appealed to a European court to have one of the major fines dismissed, but the fine was upheld by the court in mid-2012.
And in March 2013, EU regulators fined Microsoft an additional $731 million for failing to live up to an agreement to allow users of Microsoft's Windows software to easily choose a Web browser other than Microsoft's Internet Explorer.
Microsoft took responsibility for that violation, which it blamed on a "technical error."