YouTube is giving third-party clients an ultimatum: Stop blocking ads or else.

Many third-party YouTube apps offer a better experience than the official one for one simple reason—they provide an ad-free experience. YouTube has been cracking down on ad-blockers, and is now taking its fight to third-party clients.

In a support article entitled “Enforcement on Third Party Apps,” the company draws a line in the sand for third-party apps that continue to block ads.

We’re strengthening our enforcement on third-party apps that violate YouTube’s Terms of Service, specifically ad-blocking apps.

Viewers who are using these third-party apps may experience buffering issues or see the error “The following content is not available on this app” when trying to watch a video. We want to emphasize that our terms don’t allow third-party apps to turn off ads because that prevents the creator from being rewarded for viewership, and Ads on YouTube help support creators and let billions of people around the world use the streaming service. We also understand that some people prefer an entirely ad-free experience, which is why we offer YouTube Premium.

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

The news is not unexpected, but still a disappointing turn of events.