Apple will begin enforcing its new iTunes App Store rules come June 30, and Amazon’s frequent Top 100 Kindle e-reader app is likely in Cupertino’s crosshairs. At issue is the prominent “shop in the Kindle store” button that takes users out of the App Store and into a web browser from which they can search for and purchase e-books.

Apple’s new rules explicitly state that “external mechanisms for purchases … such as a ‘buy’ button that goes to a web site to purchase a digital book” are forbidden; the current “shop in the Kindle Store” option circumvents Apple collection of the 30% sales revenue fee from purchases made within the App Store.

In February, Apple removed Sony’s reader app–which remains absent from the App Store–for the same reason.

A mobile app developer who is familiar with the language of Apple’s new rules was quoted by CNN Money as saying that vendors changing the wording of the button to something such as “visit our website” would likely be permissible.

Neither Apple nor Amazon would comment to CNN Money on the potential showdown.

Read more at CNN Money ^[1].