Unless key iOS apps begin offering content or subscriptions for purchase within their App Store application, they will be no more come July 1.

This could spell the end of some of the more popular apps in the App Store, including the Amazon Kindle, Hulu Plus, and Netflix apps.

We’ve told you about this before, but now the story is picking up steam.

According to AppleInsider, this rule has always existed. Apple is now going to enforce it.

The problem, according to Apple, is that apps such as Hulu+ include links to external websites to purchase their content or subscriptions. Meaning, Apple doesn’t receive their normal 30 percent cut.

Apple is offering a compromise. Publishers can still offer digital subscriptions on their website, as long as the same products are available in the App Store application.

“All we require is that, if a publisher is making a subscription offer outside of the app, the same (or better) offer be made inside the app, so that customers can easily subscribe with one-click right in the app,” Apple Chief Executive Steve Jobs said in a statement.

So far, some publishers are balking at this plan.

According to Peter Kafka of MediaMemo, Time, Inc. is unhappy with the prospect of Apple receiving a 30 percent cut, and will probably leave the iOS platform altogether.

In the end, it is hard to see companies such as Amazon and Netflix leaving the iOS marketplace. But, for the time being, that remains a possibility.