YouTube is bringing its ad blocker fight to mobile. In an update on Monday, YouTube writes that users accessing videos through a third-party ad blocking app may encounter buffering issues or see an error message that reads, “The following content is not available on this app.”

Last year, YouTube “launched a global effort” to encourage users to allow ads while watching videos or upgrade to YouTube Premium. It also began disabling videos for users with an ad blocking extension enabled.

But now, YouTube says its policies don’t allow “third-party apps to turn off ads because that prevents the creator from being rewarded for viewership.” The block targets third-party apps that use YouTube’s API to get videos interruption-free. AdGuard says it’s not affected by the change since its app doesn’t use YouTube’s API.

“We only allow third-party apps to use our API when they follow our API Services Terms of Service,” YouTube says. “When we find an app that violates these terms, we will take appropriate action to protect our platform, creators, and viewers.”

To get around this, YouTube once again suggests signing up for the ad-free YouTube Premium. This likely won’t come as pleasant news to all the users who watch YouTube through ad blocking apps, but it doesn’t look like YouTube is backing down in its battle against ad blockers anytime soon.

Update Tuesday April 16th, 10:09AM ET: Added an update from AdGuard.