Content providers have begun to change how they sell through their apps for Apple's mobile devices.

They include The Wall Street Journal, Amazon.com and others after Apple revised the rules. On Sunday, the journal and Canadian e-book retailer Kobo said they will no longer sell content through Apple-based apps. According to Kobo, Apple indicated Saturday that it will enforce new rules that content providers may not sell from their Apple apps without giving Apple a 30 percent cut.

So from now on, to buy Kobo e-book titles, customers will need to visit Kobo's web site. Kobo titles and apps will still run on Apple's products. Similarly, the Journal will remove all e-commerce from its Apple-based apps, and customers will have to go to its web site to make an online purchase.

The Journal said it was "concerned" the new rules could "create a poor experience for our readers, who would not be able to directly manage their WSJ account" or easily obtain the Journal's content across various platforms. Amazon and Barnes & Noble, among others, have also removed e-commerce options from their Apple-based apps. Apps for the Kindle and nook e-readers no longer have a "buy" option.

Google also appeared Monday to have removed from Apple's App Store its Google Books app, which allows customers to buy content from the company's e-book store. On Tuesday, the app reappeared, although now it only allows users to sync Google-purchased e-books across devices. To buy more books, users have to go to Google Books.