The Federation of German Consumer Organizations (vzbv) has now threatened legal action against WhatsApp for passing on user information such as telephone numbers to Facebook.
"When Facebook took over WhatsApp in 2014, it pledged that the WhatsApp service would remain independent. Consumers trusted that their information would remain with WhatsApp alone and that no information would be transferred to Facebook. Their trust was broken," the consumer watchdog said in a statement on Tuesday.
According to The Local.de, it has given WhatsApp until Wednesday to issue a declaration that it will not implement the changes to user terms.
If it fails to do so, the vzbv will begin legal proceedings against the firm.
"We are extremely concerned about this insidious trend: consumers are losing step by step the ownership of their data. Their private sphere is in danger," the consumer watchdog's statement read.
According to WhatsApp, data-sharing is to the advantage of the user as they will see advertisements from companies they have already been in contact with rather than from ones they have never heard of, the report added.
The Delhi High Court has also sought a response from WhatsApp on a petition against the popular messaging app's decision to share users' data with Facebook.
A division bench of Chief Justice G. Rohini and Sangita Dhingra Sehgal asked WhatsApp to file its response on the plea filed by Delhi-based users who raised concerns over the security of their data shared using the app.
The bench asked WhatsApp to explain the facts about the issue before September 21, the next date of hearing.
"If you do not want your account information shared with Facebook to improve your Facebook ads and products experiences, you can uncheck the box or toggle the control," it added.