The European Union wants to know more about Google's collection of private information. A watchdog group that advises the European Commission on issues of privacy protection sent Google a letter today asking for more details on its policies regarding data storage.

Google keeps data from private searches for up to two years, which it says can be helpful in producing more useful search results. After 18 to 24 months, Google's search records become anonymous, which it says protects the privacy of its users.

The European Union wants to know what Google does with users' data, and whether it has taken the appropriate steps to comply with E.U. privacy laws, which are stricter than those in the U.S. The chair of the advisory group says that, based on Google's description of its policies, the company is in violation of data protection laws, Bloomberg reports.

Google consulted with European privacy regulators before making its data retention policies, according to the Wall Street Journal. It will respond to the letter before the advisory group's next meeting in June.

In April, Google announced plans to buy the internet advertising company DoubleClick, and its competitors Yahoo and Microsoft have stepped up advertising initiatives recently as well. Some regulators are concerned that the competition to deliver targeted advertising could lead to a violation of civil liberties, Bloomberg reports.