Thousands of popular Reddit communities dedicated to topics ranging from Apple Inc to gaming and music locked out their users on Monday in protest against the company's plan to charge for access to its data.

Starting next month, third-party app developers using Reddit's vast troves of data will have to pay a price and the changes could affect players across the spectrum - from deeper-pocketed companies such as OpenAI to small developers.

The Apollo app - popular among Redditors for its alternate interface to the official platform - has said the exorbitant fees have "made it impossible" to continue offering the service.

Here are some facts about the protest:

What prompted the blackout?

The action has been in the works for weeks after Reddit announced in April that it would start charging third parties for its application programming interface (API) - a software framework that allows a data provider and an end-user to communicate with each other.

From July 1, Reddit plans to charge developers that require higher usage limits $0.24 for every 1,000 API calls or less than $1 per user every month

Apollo said that with their current usage, the charges would cost more than $20 million a year.

Why is Reddit making the change?

One of the reasons is generative AI.

Reddit's conversation forums have a lot of data that can be used to train tools such as ChatGPT, the viral chatbot from Microsoft-backed OpenAI. While some of this data can be collected in an unstructured fashion, Reddit's API makes it easier for companies to directly find and collate the data.

Reddit CEO Steve Huffman said in an interview with the New York Times in April that the "Reddit corpus of data is really valuable" and he doesn't want to "need to give all of that value to some of the largest companies in the world for free."

Who gets affected and when will the Reddit blackout end?

Thousands of subreddits - the forums dedicated to a specific topic on Reddit - are protesting the move and most of their moderators have planned a 48-hour blackout during which the pages will go private, meaning millions of users will be left without access.

Subreddits such as r/Music, r/gaming, r/science and r/todayilearned - all with more than 30 million subscribers - are participating. Some like r/Music plan to protest indefinitely.

Unlike most other social media platforms, Reddit is heavily dependent on community moderators, "or mods", who police their subreddits for free to weed out offensive or illegal content.

What are third-party app developers saying?

Christian Selig, creator of the Apollo app for Reddit, last week tweeted the service will close down on June 30.

Huffman has said other third-party apps such as Reddit is Fun and Sync have also decided the new pricing "doesn't work for their businesses and will close before pricing goes into effect".

What is Reddit saying?

Huffman on Friday noted the frustration among many moderators of Reddit communities but said the company can no longer subsidize commercial entities that require large-scale data use as it needs to be a "self-sustaining business".

What are other social media companies doing?

Elon Musk's Twitter in January restricted all third-party clients and apps and updated their rules for developers accessing its APIs.

The new rules said that developers cannot use the company's API to create "a substitute or similar service or product to the Twitter Application."

(Reporting by Tiyashi Datta, Akash Sriram and Jaspreet Singh in Bengaluru; Editing by Devika Syamnath)