Google contends the move simplifies and unifies its policies across its various services such as Gmail, YouTube, Android mobile systems, social networks and Internet search.
"The new policy doesn't change any existing privacy settings or how any personal information is shared outside of Google," Google privacy chief Alma Whitten said on the Google Blog Thursday.
But critics including European privacy agencies and US consumer watchdogs argued the new policy, which offers no ability to opt out aside from refraining from signing into Google services, gives the Internet giant unprecedented ability to monitor its users.
"Google isn't telling you about protecting your privacy. Google is telling you how they will gather information about you on all its services, combine it in new ways and use the fat new digital dossiers to sell more ads. They're telling you how they plan to spy on you. It's a spy policy."
A coalition of European and US consumer advocacy groups made a last-ditch appeal to Internet search and advertising giant Google on Wednesday to delay the changes.
In a joint letter to Google chief executive Larry Page, the Trans Atlantic Consumer Dialogue urged Google to delay implementation of the changes, saying it would "combine data from all of your services… into a single profile without user consent and without any meaningful opportunity for users to opt-out."
The French consumer data protection agency CNIL warned this week that Google may be in violation of European privacy norms.
"The CNIL and the EU data protection authorities are deeply concerned about the combination of personal data across services: They have strong doubts about the lawfulness and fairness of such processing," a letter from the French agency said.
US Federal Trade Commission chairman Jon Leibowitz has said Google is forcing users to make a "brutal choice" — ending its use of the service or complying with the new monitoring scheme.
Google announced in January it was revising its privacy policies and changing how it uses data from users of its services to provide more personalized search results and advertisements.
The Mountain View, California-based Google said the changes are designed to improve the user experience across the various Google products, which range from Web search to Gmail to Google+ to YouTube.
The new terms will allow Google to regroup data from several different services that were previously separate under a single comprehensive profile, giving it a more integrated view of its users, an advantage enjoyed by Apple and Facebook.
"So in the future, if you do frequent searches for Jamie Oliver, we could recommend Jamie Oliver videos when you're looking for recipes on YouTube — or we might suggest ads for his cookbooks when you're on other Google properties.