Three of China’s biggest internet firms are being investigated by the country’s Cyberspace Administration.

The firms – Tencent, Weibo and Baidu – are all accused of violating China’s cybersecurity laws.

“Users are spreading violence, terror, false rumors, pornography and other hazards to national security, public safety, social order,” the administration said in a statement.

For those that are unaware, internet access in China is heavily censored with access to sites such as Google and Facebook being heavily restricted. While the aforementioned tech companies do offer services similar to that of Facebook and YouTube, the services are heavily monitored.

This monitoring has been ramped up ahead of the 19th National Congress of the Communist Party of China happening later this year.

Despite the heavy censorship and monitoring there is still dissent that appears online and Fortune reports that just last month authorities warned the firms to clean up rumours about party officials and other illicit content on their sites.