Popular e-reader apps from major e-book retailers such as Amazon and Barnes & Noble have been forced to comply with Apple’s latest crackdown on in-app purchases made outside of its App Store model.

CNet News reports that Apple twice last month amended its terms for subscriptions in the App Store in bid to ensure that all in-app purchases were subject to Apple’s usual 30 percent revenue share. Previously, many apps – especially e-reader apps – were able to send customers to a web-based interface outside the app to buy new content, meaning Apple missed out on its cut.

According to the report, Amazon, Barnes & Noble, and Canada-based Kobo have all updated their iOS e-reader apps, with Barnes & Noble temporarily removing its ‘Nook for iPad’ app from the App Store. The new versions allow content to be stored and accessed from the iOS device library but require new e-books to be manually bought at the respective company’s websites and then synched. Purchases via Apple’s own iTunes store are, of course, still allowed within the app.

“Aside from not having any links to an e-bookstore, you can’t even mention your website or explain to readers from within the app how to purchase books and get them onto the device,” Kobo CEO Michael Serbinis told CNet News. “It’s very simple to do, but some people downloading the app for the first time might not figure it out.”

Both Amazon and Barnes & Noble have their own e-reader devices, the Kindle and Nook, respectively. 

The new regulations also affect subscription services such as newspapers and periodicals. According to the report, the Wall Street Journal has announced that it will soon remove all purchasing options from with its iOS apps to comply with Apple’s new rules. Others – notably the Financial Times – are attempting to migrate away from Apple entirely, promoting browser-based versions of their content.