Amazon.com's Kindle apps for iPhone and iPad appear to run afoul of the rules laid out today by Apple as part of its new in-app subscription and content purchasing system.

Apple said in the announcement that companies "may no longer provide links in their apps (to a web site, for example) which allow the customer to purchase content or subscriptions outside of the app."

As it happens, the rule describes precisely what Amazon currently does in its Kindle apps -- providing a "Kindle Store" button that switches users out of the app to the device's browser, where they can make the purchase. Gregg Keizer of Computerworld confirmed with Apple that the rule applies not only to subscription-based purchases but also to content sellers such as Amazon.com.

[Follow-up Rhapsody ready to fight Apple over new in-app subscription rules]

The rule is designed to ensure that Apple gets its 30 percent cut of the sale prompted by the app.

“Our philosophy is simple—when Apple brings a new subscriber to the app, Apple earns a 30 percent share; when the publisher brings an existing or new subscriber to the app, the publisher keeps 100 percent and Apple earns nothing," said Apple CEO Steve Jobs in the news release announcing the new service.

We've reached out to Amazon for comment, to find out what it plans to do, and we'll update this post depending on the response.