Xi Jinping’s media crackdown isn’t letting up.

After Wujie News published an anonymous letter calling for President Xi Jinping’s resignation, a total of 16 people that worked with online media outlet have gone missing, the BBC reports.

According to an unnamed source speaking to the British news site, a senior manager, a senior editor, and four other employees have been detained by police. 10 other people that work with “a related technology company” have also been taken away.

A mainland Chinese journalist living named Jia Jia was also went missing in Hong Kong last week, just as the article was spreading online. According to a friend of Jia, he did not write the letter personally and simply contacted the news outlet to remove the article. His lawyer has since told media that he has been detained by Chinese police.

It is unclear whether Wujie published the letter on purpose or was hacked—publishing such a letter would be tantamount to political suicide for its backers, which include Alibaba and the government of Xinjiang province.

The open letter is harshly critical of several specific characteristics of Xi’s rule, including his anti-corruption campaigns and emerging cult of personality:

In the political sphere, your abandonment of important Party tradition, including most significantly the abandonment of the democratic system of the collective leadership of the Standing Committee, instead having all leaders at all levels support your position at the “core,” has resulted in an excessive concentration of power. While strengthening the power of the Party Committees within the NPC, CPPCC, and the State Council, you’ve weakened the independent power of all state organs, including that of Premier Li Keqiang and others.

In recent weeks, Xi has asked state media to declare its loyalty to the ruling Communist Party and to him. A February editorial published in China Daily, an English-language party mouthpiece newspaper, argued “It is necessary for the media to restore people’s trust in the Party, especially as the economy has entered a new normal and suggestions that it is declining and dragging down the global economy have emerged.”