Facebook has run into a fresh attack from privacy activists after the huge social network modified policies on how it manages users' data.
Additionally, the changes make it easier for advertisers and others to send messages on Facebook, limiting users' control, according to privacy rights groups.
Activists have raised a ruckus over the changes, saying they could violate some laws or Facebook's agreement with US regulators earlier this year after complaints from privacy groups.
The latest spat highlights Facebook's quandary on how it can monetize data from its billion users worldwide by sharing information and still live up to its pledge to protect privacy.
Facebook's stock price has slumped more than 30 percent since its hotly anticipated market debut in May, in part due to concerns overs this problem.
Two groups this week sent a letter to Facebook chief executive Mark Zuckerberg asking him to roll back the changes.
The Electronic Privacy Information Center and Center for Digital Democracy said in the letter that they found the changes announced November 21 "troubling."
"Facebook's proposed changes implicate the user privacy and the terms of a recent settlement with the Federal Trade Commission," said the letter signed by EPIC's Marc Rotenberg and CDD's Jeffrey Chester.
"The settlement prohibits Facebook from misrepresenting the extent to which it maintains the privacy or security of covered information. Additionally, prior to any sharing of users' personal information with a third party, Facebook must make a clear and prominent disclosure and obtain the affirmative express consent of its users."
The letter said the end of the voting element terminates Facebook's pledge of "an open and transparent system of governance."
It said the changes also would limit users' ability "to prevent strangers from sending unwanted messages," and thus are "likely to increase the amount of spam that users receive."
The activists added that sharing information between Instagram and the main Facebook site reneges on an agreement to keep the unit independent.
Other activists also raised protests.
"The proposed changes are bad for users," said John Simpson of Consumer Watchdog.
"It takes away their right to be involved in privacy changes and allows Facebook to share data with affiliates in ways that it had not previous done. The changes clearly violate Facebook's consent agreement with the FTC and European data protection laws."
Simpson said Facebook "should withdraw the changes immediately or the FTC and European regulators must take strong action."
Facebook on Tuesday declined to comment on the criticism.
In unveiling the changes last week, Facebook said the system of user voting was not working as intended.
"We deeply value the feedback we receive from you during our comment period," Facebook said in a message to users, while adding that the vote system "resulted in a system that incentivized the quantity of comments over their quality."
"Therefore, we're proposing to end the voting component of the process in favor of a system that leads to more meaningful feedback and engagement," Facebook said.
The company has since grown to more than a billion users, moved to the former Sun Microsystems campus in the city of Menlo Park, California, and raised billions of dollars by going public with its initial public offering of stock in May.
Facebook said it was still considering feedback from its members through Wednesday, before finalizing its policies.
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