(Tony Avelar/Bloomberg)

The European investigation coincides with a separate investigation by the U.S. Federal Trade Commission, the first major antitrust investigation of the Internet sector. Many antitrust experts say the E.U. investigation could set the tone for the U.S. probe.

The E.U. office responsible for competition policy said it sent a letter to Google Chairman Eric Schmidt saying it found the firm appeared to display links for its own services in a way that favored their own travel and restaurant services, for example, over competitors’ sites.

“We are concerned that this may result in preferential treatment compared to those of competing services, which may be hurt as a consequence,” said Joaquin Almunia, vice president of the European Commission responsible for competition policy.

The firm also allegedly copied content such as user reviews from competing search engines without permission, which could reduce a competitors’ incentive to invest in original content, according to the European Union.

The antitrust enforcement office said Google appeared to shut out advertising competition and made it hard to use its ad service on other software platforms.

Almunia asked Schmidt to respond within “weeks.”