Facebook has been censoring Chinese users since the end of May.
Chinese users are being told that they need to be logged in to their social media accounts to use Facebook or use their accounts to access other services, including VPNs.
Facebook’s latest move, to require users to sign in, will effectively stop Chinese users from accessing Facebook and other social networks, in order to prevent people from circumventing the censors’ controls.
But, Facebook’s move has also been criticised as being unfair and a breach of China’s user rights.
Some have called the move discriminatory.
The company has also warned Chinese users that their accounts will be suspended if they do not comply.
Facebook has not said why the ban is being imposed.
Chinese internet users are increasingly worried about social media in China, where they are increasingly censored.
In May, Facebook blocked a Chinese social media platform called WeChat after the company said it had found it to be violating its terms of service.