Proposed changes to an upcoming version of Chrome could mean that popular blockers, such as uBlock Origin and uMatrix “can no longer exist,” say the makers of those extensions.

The proposed changes, made public in a Google document, would replace a key API ad blocking software developers rely upon for their extensions to work.

“This would basically mean that Google is destroying ad blocking and privacy protection as we know it,” ad block developer Ghostery said in a statement to Gizmodo. “Users would be left with only very limited ways to prevent third parties from intercepting their surfing behavior or to get rid of unwanted content.”

Google says the proposed changes were made to increase “security, privacy, and performance for extensions.” As more and more developers object to the changes, though, the company is slowly walking back from the proposal.

“This design is still in a draft state, and will likely change,” said Devlin Cronin, a Google software engineer on a message board discussing the changes. “Our goal is not to break extensions. … Having a list of the use cases that aren’t feasible is incredibly useful for us in moving forward.”

Ad blocking software is unpopular with many websites that rely on online ads for revenue. Proponents of the technology, though, say it prevents companies from tracking consumers on the web and is a key shield for people’s privacy.

Google, historically, has sided with ad blocking technology In 2017, it added features to Chrome that blocked certain ads based on content, despite some criticism from companies.