Apple has started sending notices to developers who offer apps in China with CallKit integration. The notice explains that apps cannot offer CallKit functionality in China due to government regulations. In order for developers to make their application available on the China App Store, they must remove that CallKit integration. Alternatively, they can remove the application from China altogether.

This crack down appears to have been a long time coming. Popular communication app WeChat briefly supported CallKit integration, though the feature was later removed.

Apple’s App Store has had several issues in China throughout recent years. Last summer, Apple was forced to remove VPN applications from the App Store in China in order to comply with local laws. That move was met with criticism from users, as well as a handful of U.S. lawmakers who criticized the company for conforming so quickly to a request from the Chinese government.

On a broader scale, Apple has been removing applications in China at a much faster pace than normal, according to a study last year.

CallKit was introduced in iOS 10 as a way for developers to integrate calling services with other call-related applications. Here’s how the company describes the framework:

The Chinese government likely takes issue with the VoIP functionalities of CallKit. Such services are frowned upon in the country. Apple removed the Skype application last summer for a similar reason.

However, Apple’s crackdown this time around seems to be blankety related to CallKit, as even applications that use the functionality to pause audio for an incoming call have been removed.