The US Electronic Privacy Information Center (EPIC) has asked the Federal Trade Commission (FTC) to halt Facebook's $19bn proposed acquisition of WhatsApp, saying that the deal would harm WhatsApp users by permitting their data to be sucked into Facebook's advertising business.
The acquisition is said to be Facebook's largest acquisition to date as the social networking tried to increase its popularity among younger users.
EPIC has requested the commission to initiate an investigation of the proposed deal and to block it until any privacy issues are resolved.
Reacting to the filing, Facebook said: "As we have said repeatedly, Whatsapp will operate as a separate company and will honor its commitments to privacy and security."
EPIC said the FTC has previously responded favorably to its complaints concerning Google Buzz, Microsoft Passport, changes in Facebook privacy settings, and Choicepoint security practices.
The FTC has however approved Google's acquisition of Doubleclick, which EPIC had objected to.
Facebook is currently under a 20 year consent decree from the FTC that requires the social media firm to protect user privacy and to comply with the US-EU Safe Harbor guidelines.