One of China’s most popular messaging apps, WeChat, has started shutting down certain accounts known for their political writings, the latest sign that the nation is stepping up its censorship of the Internet.

Chinese users began noticing the closures on Thursday, as several public accounts on WeChat went silent. Users trying to access them were instead met with a message that said the accounts had violated WeChat policies.

Tencent, the Chinese Internet giant behind the social networking platform, said the account closures were made to ensure a quality user experience. “We continually review and take measures on suspicious cases of spam, violent, pornographic and illegal content. We also welcome users to report to us online or through our 24-hour hotline,” the company said in an email.

But many of those closed accounts come from publications and local scholars that write about the nation’s politics. Some have published articles critical of China, and examined government corruption and the nation’s one-party rule.

“May I ask which article I wrote touched a nerve? What law did it violate? Who complained?” wrote Xu Xin, a legal scholar, in a posting on Chinese social networking site Sina Weibo.

WeChat has close to 300 million users, and has risen to become one of the hottest mobile app products in the nation. Along with providing messaging services, the product has become a social networking service, where users can share posts and pictures with friends.

To help certain users, such as businesses, promote their brands on WeChat, the service created so-called “public accounts” that any user can subscribe to.

The recent crackdown on public accounts, however, is no surprise. In November, China specifically named WeChat as among the social networking services it wants greater control over. Authorities are particularly concerned at the way the services can rapidly spread information, adding that they could be used to destabilize the country.

China’s other major social networking site, Sina Weibo, has faced similar scrutiny. The nation has spent the past two years cracking down on alleged “rumors” and fake information circulating on the Twitter-like platform, by deleting accounts and even jailing users in some instances.