Internet users in China can face up to three years in jail if messages posted by them are deemed “slanderous” and found to have been “retweeted” or forwarded more than 500 times, according to regulations put into effect on Tuesday.

The rules were outlined in a judicial interpretation issued by the Supreme People’s Court.

The measure has evoked concern among Internet users, and has been widely seen as the latest attempt yet by the Communist Party of China (CPC) to rein in the increasingly vibrant online community. The regulation does not spell out what authorities might deem to be slanderous and bloggers fear it will be used to blunt any criticism aimed at the government.

The proliferation of Twitter-like social media platforms such as Sina Weibo, which has more than 500 million users, has posed a challenge to the CPC’s control over information, with microblogs increasingly shaping public discourse.

In 2009, the government closed down the then popular Fanfou microblog following ethnic riots in Xinjiang, which some officials saw as being partly triggered by photographs circulating online. The government subsequently allowed the introduction of other microblogs, or Weibos, run by companies such as Sina and Tencent, but introduced a system to monitor and censor content.

The unprecedented spread of Weibo has, however, provided the authorities with an increasingly difficult challenge to shape public discourse. That Tuesday’s regulation was especially aimed at citizens who pose a danger to “social stability” was indicated by comments made by the Supreme People’s Procuratorate, the top investigation and prosecuting agency.

“Some Internet users fabricate rumours about others and create false information while making use of sensitive social issues, which has disrupted social order and triggered mass incidents,” spokesman Sun Jungong was quoted as saying by the official Xinhua news agency.

The move comes amid a campaign to crack down on online rumours . In recent days, authorities have brought together public figures who are prominent “opinion leaders” on websites such as Sina Weibo and reminded them of their responsibilities in helping authorities “guide public opinion”.

Last month, investor and businessman Charles Xue, an outspoken commentator with 12 million followers on Sina Weibo, was detained by police during a prostitution raid. The prominent coverage of his detention by State media outlets has, however, led some bloggers to suggest the move was a warning shot aimed at outspoken public figures.

Also last month, Liu Hu, a journalist in Chongqing, was detained after he called on authorities to investigate a provincial official.

Bloggers have come to see social media as the only platform that allows for discourse not controlled entirely by the State media apparatus.

“What if the rumours come from the Xinhua news agency or China Central Television [the State broadcaster],” asked blogger Ge Jia on Tuesday. Peking University law professor He Weifang, a prominent critic of censorship, wrote to his one million followers on Weibo, “Please don’t retweet me over 500 times, and let me survive.”