The letter, dated today, was signed by the chairman of the EU's Article 29 Working Party and other officials. They say that Google should "develop new tools to give users more control over their personal data."
The EU launched its inquiry into Google's privacy practices after the company announced it would start aggregating data about users across a variety of platforms -- including Android, Gmail and YouTube. That shift applies only to users who are signed in.
Google says that the new policy allows it to target ads and search results more precisely by drawing on a broader pool of information about users than in the past. The company isn't collecting any additional data or sharing information with outsiders.
Google has always maintained that its new policy -- which took effect on March 1 -- doesn't pose any new privacy risks. But EU officials see things differently.
"Google did not set any limits to the combination of data nor provide clear and comprehensive tools allowing its users to control it," the letter states. "Combining personal data on such a large scale creates high risks to the privacy of users."
The officials recommend that Google clarify how it combines data and also that it "develop new tools to give users more control over their personal data."