On Tuesday, we reported that Sony’s eBook reader app for iOS had been rejected by Apple. The reason Apple gave for the rejection was that Sony’s app violated an app store policy — one that has historically not been enforced — dealing with apps that offer content for sale through means other than Apple’s in-app purchase mechanism. By using their own distribution systems, developers have been able to sell content from within iOS apps without having to pay Apple’s 30% commission charged for iTunes-based in-app purchases. An Apple spokesperson later gave a comment, stating that Apple is “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.” Following the ordeal, The Wall Street Journal on Wednesday reports that developers have begun to receive notices that apps in violation of this policy will be rejected starting March 31st. This could mean existing apps like Amazon’s Kindle eBook reader, which sends users to a mobile website in order to make purchases, could run into problems unless they are updated to offer content through iTunes. According to the Journal, the only exception to the rule that will be made is for publishers wishing to give print subscribers free access to an iPad edition.