Search engine accused of opaque data collection strategy.
EU data regulators are pressuring Google to become more transparent about what data it collects and divulges.
The dispute follows the search engine’s 2012 consolidation of more than 60 privacy policies across services including YouTube, Google Maps and Gmail.
Writing to the firm’s chief executive Larry Page, the EU’s Article 29 Working Party said: "Google must meet its obligations with respect to the European and national data protection legal frameworks and has to determine the means to achieve these legal requirements."
Data protection across the EU is handled by national agencies, with multinational firms scrutinised by the country in which their European head office is quartered.
Europe places a greater emphasis on a right to privacy than the US, and has recently instated a number of controversial measures, including a right to have "irrelevant news" articles removed from search engines, called "the right to be forgotten".
Anna Fielder, chairwoman of trustees at Privacy International, told the BBC that the EU’s data protection rules were "fundamental basics" that should have been implemented years ago, adding that the speed of developments was "shameful".