CNIL, which is acting on behalf of a group of European data watchdogs, has given the search and advertising company until 5 April to respond to the probe.
Google said that it had received the CNIL letter in a statement on Monday.
Google said the policy "provides all the information required in Articles 10 & 11" of the European Data Protection Directive, and "it follows the guidelines published by the Article 29 Working Party in 2004." The guidelines (PDF) concern "more harmonised information provisions" for implementing the directive.
Google updated its policy on 1 March despite requests from European data authorities to postpone its implementation. People cannot opt out of having their data shared across Google services to target advertising, leading campaigner Alex Hanff to seek compensation.