YouTube has long been acutely aware of how important advertising revenue is. As an ad-supported video-on-demand (AVOD) platform, YouTube depends on money from ads to continue being able to offer its video hosting services for free. That’s why The Verge reports that YouTube is testing a function that pulls up a prompt for users with ad-blockers installed, telling them they could be shut off from the platform unless the blocker is disabled.

The tests indicate that viewers will be blocked from YouTube if they watch three videos in a row while having ad-preventing software installed. Users will be prompted to sign up for YouTube Premium if they prefer to go ad-free; YouTube Premium costs $11.99 per month, or $119.99 annually.

YouTube is clearly looking for ways to expand the user base on its Premium service. Last October, the company performed an experiment in which it placed the ability to stream Ultra-High-Definition 4K videos behind the Premium paywall. YouTube eventually restored the ability to stream 4K videos to free users, but just this month it began testing a higher-bitrate 1080p visual quality that is so far only available to Premium subscribers.

One of the problems the entertainment industry is dealing with as a whole currently is the softness of the advertising market. Most advertisers are struggling these days, and when advertisers struggle revenues become harder to come by. That hurts advertisers and TV and streaming providers who rely on such revenue, which is likely part of the reason YouTube is taking a harder line on ad-blocking software now.