Google is being investigated by the EU following complaints from price comparison sites.
British price comparison site Foundem and French legal search engine ejustice.fr approached the European Commission about "unfavourable treatment of their services in Google's unpaid and sponsored search results coupled with an alleged preferential placement of Google's own services", the EU said.
The two websites believe Google lowered the rankings of the sites in its results.
"The European Commission has decided to open an antitrust investigation into allegations that Google has abused a dominant position in online search," the Commission said.
The Commission also plans to investigate allegations of 'exclusivity clause' that meant sites carry adverts served by Google could not feature advertising from rival search engines.
The EU said it currently has no proof Google has infringed any antitrust legislation.
Google said since the search engine started it has "worked hard to do the right thing by our users and our industry. But there's always going to be room for improvement, and so we'll be working with the Commission to address any concerns."
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