Apple's apparent attempt to clamp down on discussion about the rejections was first reported by the Apple-focused news site MacRumors.com. The warning reads, "The information contained in this message is under non-disclosure," according to the site.
MacRumors points out that Apple's conditions for submitting applications for inclusion in the App Store may already include the NDA, but Apple apparently feels a need to make it clear.
Apple had not responded to an interview request at the time of this writing.
The App Store is where iPhone and iPod Touch users can go to choose from thousands of applications from third-party developers. The software must be approved by Apple before it's offered. As a gatekeeper, Apple has been criticized for being inconsistent in its rationale for rejecting applications. In some cases, applications that have been approved are later pulled.
Among the high-profile applications rejected was the iPhone Podcaster, which helps users download and organize podcasts. Apple rejected the application because it duplicated functionality in the desktop version of iTunes, according to the developer.
"I find this a bit strange considering there are numerous apps that duplicate the functionality of other apps," the developer said in his blog.
Apple's approach to the App Store differs greatly from the soon-to-launched Android Market for mobile phones built with the Google-led Android open source operating system. The expected no-approval process, however, has raised concerns about whether the most useful applications will get in front of visitors and whether malware and spam can be filtered out.