Over 800 subreddits have announced plans to go “dark,” making their content inaccessible to users on June 12 and 13 (and in some cases longer)—and the number continues to grow rapidly. Included among the list are r/gaming, r/pics, and r/todayilearned, all of which have more than 30 million subscribers each.

r/wallstreetbets, which has had a profound impact on the stock market over the past few years, will also take part in the protest.

At issue is Reddit’s decision to impose charges on certain third-party apps to utilize its application programming interface (API), a tool that powers popular tools like Narwhal, Apollo, and Infinity, which give users an alternate way to browse Reddit’s forums.

“This collective action is intended to raise awareness and urge Reddit to reconsider their recent API changes,” read a message on r/pics. “Our primary goal is to initiate a productive dialogue with Reddit, leading to a reversal of the detrimental modifications they have implemented. We understand that this blackout may cause temporary inconvenience to our community, and for that, we apologize. However, we firmly believe that this short-term disruption will bring long-term benefits for every user.”

Reddit first announced changes to its API policy in April, but the ramifications of that weren’t clear until earlier this month. The founder of the Apollo app posted on Reddit that in order to keep that business running as is, it would have to pay Reddit $20 million per year. And a developer for RIF, another third-party reader, said the changes to the API policy “will likely kill” his app and others.

Reddit has said it is charging the fee for its API to cover the costs of an ad-free experience.

While most of the subreddits plan to stay dark for two days, others (including r/music) say they will stop operating “indefinitely,” since they say moderators are unable to do their work with the tools on Reddit’s official app.

When asked for comment, a Reddit spokesperson told Fortune: “We’re in contact with a number of communities to clarify any confusion around our data API terms, platform-wide policies, community support resources, and timing for new moderator tools…We’re committed to fostering a safe and responsible developer ecosystem around Reddit—developers and third-party apps can make Reddit better and do so in a sustainable and mutually beneficial partnership, while also keeping our users and data safe.”