YouTube could crack down on ad blockers. That won’t be a popular decision.

For as long as YouTube pre-roll ads have existed, users have attempted to block them. Software programs like AdBlock Plus and AdBlock Pro have attracted millions of users by turning YouTube into an ad-free experience.

Though YouTube has never expressed support for ad blockers, it has not taken serious steps to restrict them — until now. Some users on the Google video platform are seeing a message that says ad blockers are “not allowed.” In lieu of popular third-party programs, YouTube wants its users to pay for YouTube Premium, which costs $11.99 per month and offers ad-free browsing as one of its primary perks.

As seen in the above image, YouTube’s warning message is targeting users who have ad blockers installed on their internet browsers. The platform is asking its community to consider the impact of ad blocking: “Ads allow YouTube to stay free for billions of users worldwide,” the message reads.

By some estimates, publishers lost $22 billion in a single year thanks to ad blockers — and that was nearly a decade ago. Adoption of ad blockers has only increased since then. Adblock for YouTube has received more than ten million installs on Google Chrome, while AdBlocker for YouTube

reaches 500,000 users on Firefox.

In a more recent survey, 61% of respondents said they would be unlikely to return to a website if it disabled their ad blocker without their consent. YouTube is now calling that bluff, and as a result, it has invited a slew of critical tweets from software developers, viewers, and creators. Meanwhile, some indignant viewers are highlighting pieces of software that block attempts to block ad blockers (say that three times fast).

YouTube has confirmed that it is testing anti-adblock messaging. “We’re running a small experiment globally that urges viewers with ad blockers enabled to allow ads on YouTube or try YouTube Premium,” a company spokesperson told BleepingComputer. “Ad blocker detection is not new, and other publishers regularly ask viewers to disable ad blockers.”

So far, YouTube has gotten one clear result from its experiment: If it ever institutes a full-scale crackdown on ad blockers, it can expect a lot of angry users in its comment sections.