In China, the censoring laws are pretty strict. Many of the services that we use in the western part of the world are blocked by the firewall in China. That includes every service Google has, Twitter, Periscope, Facebook, Instagram, Snapchat, and a ton of others. Wikipedia was blocked until recently. WeChat is a very popular messaging app over in China, in fact it has over 10 million downloads. But there are some other popular messaging apps that people are using that are not made for China. Like WhatsApp, and according to the New York Times, the government is shutting down mobile service for those using those apps.
Users receive a text message before their service is shut down, stating "Due to police notice, we will shut down your cellphone number within the next two hours in accordance with the law. If you have any questions, please consult the cyberpolice affiliated with the police station in your vicinity as soon as possible." Currently this is only happening in Xinjiang, which isn't as big of a tourism area as Beijing or Shanghai. Xinjiang is in northeastern China, near Kazakhstan.
Additionally, it's being reported that the police are not only shutting down users of these apps, but also those who are using VPN's and those who have failed to register their account with the proper identification. Now it's worth noting that WhatsApp is not blocked by the firewall in China. Which makes it a bit interesting as to why the government is shutting down service of those using WhatsApp in the mainland. Although, it's likely going to be blocked in the near future.
Xinjiang has cracked down on censorship action before. Following riots in 2009, the internet was shut off for nearly six months. This also isn't the first time the government has cracked down on messaging apps. China has already cracked down on VPN's being used in the country. VPN's are typically used to bypass the firewall and be able to use services that are blocked in China, while in China. Essential to tourists that are a custom to using Google Maps, Gmail, Twitter, or Facebook. China takes their censorship very seriously, and they are the only country that takes it this far.