YouTube appears to be stepping up its long war on ad blockers this week. The creator of SponsorBlock, a crowdsourced ad blocker, posted a tweet on Wednesday claiming YouTube is experimenting with server-side ad injection. This would inject ads directly into a video’s stream, and render many ad blockers useless.

“YouTube is improving its performance and reliability in serving both organic and ad video content,” said a Google spokesperson in an emailed statement to Gizmodo, when asked if it was injecting server-side ads. “This update may result in suboptimal viewing experiences for viewers with ad blockers installed. Ad blockers violate YouTube’s Terms of Service, and we’ve been urging viewers for some time to support their favorite creators and allow ads on YouTube or try YouTube Premium for an ad-free experience.”

The introduction of server-side ads only seems to be affecting a few users for now, but it appears to be YouTube’s latest hit in its long war on ad blockers. As Bleeping Computer explains, YouTube has traditionally performed client-side ad injection, where the ads and video came to your desktop or mobile app separately. Then your video player is programmed to inject ads throughout. Traditional ad blockers identify this programming and navigate around it.

Some affected users took to the r/youtube subreddit to complain about the new feature. One Redditor claimed they received 90 seconds of unskippable ads before every video. Others went on X to share their grievances, noting that the server-side ads disable playback controls when playing.

With server-side ads, the ads are injected into a video before it comes to your desktop or mobile app. That breaks most ad blockers and could make it difficult to watch YouTube videos if you have one installed. SponsorBlock later noted that that it set up a server to detect when server-side ads were occurring, and rejecting submissions to prevent its database from being corrupted.

Google maintains that these ad blockers hurt the YouTube ecosystem, claiming that a majority of ad revenue goes to paying out creators. However, it’s also a major way YouTube itself makes revenue. Previously, Google tormented users with ad blockers by making videos unplayable and showing a never-ending loading screen. Another time, it delivered users an immovable prompt to disable the adblocker.