Apple has moved to stop potential e-book competitors from having access to their application store.In an announcement yesterday Apple rejected a Sony reader application from its App Store, telling the company it “can no longer sell content, like e-books, within their apps, or let customers have access to purchases they have made outside the App Store,”

The New York Times reported that the Sony Reader application lets users purchase e-books directly from its Sony Reader Store. Apple’s new requirement could also affect Amazon.com, Barnes & Noble, or other firms such as Borders selling goods via their mobile apps.

Should these applications adhere to the new requirement, Apple would receive a 30% cut of all of their sales.

Apple appears to have clarified its stance, noting that apps that offer direct sales outside of Apple must now also offer the same items for purchase within the applications, via Apple.

“We have not changed our developer terms or guidelines,” Apple spokesperson Trudy Muller told Ars Technica.

“We are now requiring that if an app offers customers the ability to purchase books outside of the app, that the same option is also available to customers from within the app with in-app purchase.”