In a joint letter to Google chief executive Larry Page, the Trans Atlantic Consumer Dialogue (TACD) urged Google to delay implementation of the changes which are scheduled to take effect from Thursday.
"On March 1, you propose to combine data from all of your services, provided by your users in very different contexts and for very different reasons, into a single profile without user consent and without any meaningful opportunity for users to opt-out," the TACD letter said.
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"This move has been widely criticized by US lawmakers, US Attorneys General, European lawmakers, European privacy officials, technical experts, and privacy organizations," it said.
"The President of the French CNIL, on behalf of European privacy agencies, has said this week that the change will violate European Union data protection law," the TACD said.
"Going forward with this plan will be a mistake. We ask you to reconsider."
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.
The TACD urged Google to "simply and directly" suspend the plan.
"Consumers have supported your products with the revenue that their interests create for you and your advertisers," it said. "You have also acquired a great deal of consumers' personal information.
"You record virtually every event of a Google user, in far more detail than consumers understand," the TACD said. "It is both unfair and unwise for you to 'change the terms of the bargain' as you propose to do."
Announcing the changes in January, Google said they will make the company's privacy policies "simpler and more understandable" and will "make our users' experience seamless and easy by allowing more sharing of information among products when users are signed into their Google Accounts."
