From March 1, data from an individual user can be shared between the company's services, which include the search engine, YouTube, Blogger and Gmail.
The company could build a highly-personal profile of anybody logged in to their account - although it says it will not collect information on someone's sexual orientation, religious beliefs or health status.
French regulator CNIL wrote to Google chief executive Larry Page warning its "preliminary analysis" showed it did not meet the requirements of the European directive on data protection.
It called for the company to pause the rolling out of the policy.
Google will use the data to target advertising far more effectively, attracting a higher price from advertisers.
It has been alerting account holders for the past six weeks about the change. But a civil liberties group has warned nine out of 10 users have not read the new rules.
Emma Carr from Big Brother Watch told Sky News: "People don't realise just how big this is. The policy document is not clear and people don't understand the change.
"All the information will be amalgamated in one profile. This is putting advertisers' needs first."
Users can restrict Google's access to their web activities by signing in to their account, going to the Web History page, clicking the "remove all Web History" button and finally confirming the opt-out.
Google will still be able to collect and store information for internal purposes. After 18 months that data will be partially anonymised.
The company will also still have to give up any web search data demanded by governments or law enforcement agencies through the courts.
Google said the changes will allow it to provide a "seamless experience" across its services, and invited EU data protection agencies to discuss the changes.
Google lawyer Peter Fleischer said: "Over the past month we have asked to meet with the CNIL on several occasions to answer any questions they might have, and that offer remains open.
"We believe we've found a reasonable balance between the Working Party's recommendations: to "streamline and simplify" our policies while providing "comprehensive information" to users.