Facebook and Google are at it again, and application developers are getting caught in the crossfire.

Facebook created last week an official list of acceptable ad providers that developers can use to make money with their Facebook applications. Notably absent from the list is Google's popular AdSense service, an omission that has developers on various forums up in arms. Also missing: Amazon.com, which offers an advertising API.

Google and Amazon apparently didn't make the list because they refused to sign on the dotted line of Facebook's new and arguably restrictive terms of service for ad providers. In short, advertising providers are forbidden from receiving, directly or indirectly, any type of Facebook user data, even if a Facebook user consents to sharing it. Should any such data end up in an ad provider's stores, the provider is required to alert Facebook immediately and purge said data.

The list isn't finalized, so it's entirely possibly Google and Amazon will sign on. But given the recent spats between Google and Facebook over sharing user data as they fight to grab the most user eyeballs, it's tough to predict who is going to blink first.

As it stands, developers are expressing outrage that they're no longer permitted to use AdSense and Amazon. "I hope you don't expect us to put our money into small startups from the approved list, simply because they are unable to supply enough inventory or haven't earned their reputation yet," wrote developer Anatoly Lubarsky on the Facebook Developers forum. "Regarding larger companies on the list: Most of them have a very bad track record."

Lubarsky and others observed that users and developers could end up suffering if developers move to lesser-known, less reliable providers. "It downgrades the user experience from Amazon and Google AdSense ads to badly designed intrusive ads from 'approved' companies," he wrote.

Other commentators observed that forcing developers to switch to unreliable ad providers could have undesirable long-term ramifications on the quality of apps that make it to Facebook. "Now that Google has been axed, we have to find an alternative. If the alternatives don't pay as well, then developers will get discouraged from developing on Facebook," read a post from username vincenz2004.

There's also a passionate discussion taking place at Hacker News. One of the participants, with the username wheels, says the move is emblematic of "the changing landscape of ever more tightly controlled 'platforms' [such as Facebook]. It used to be that the way software interacted with a platform was via APIs; now it's increasingly in alignment with the platform owner's business goals as well."

"When Microsoft crushed Netscape, it did so by controlling the platform and making the alternative seem unnecessary, but it would have been unthinkably brutish for them to disallow another browser," he wrote." But what the App Store and Facebook are doing makes Microsoft's actions look positively charitable."

Whether Google or Amazon will bow to Facebook's terms remains to be seen. Developers are going to struggle in the short term as they're forced to acclimate to a different provider, though the standoff could give other ad providers out there a chance to shine, thus opening up more choices to developers.

This story, "Developers rage after Facebook blocks Google AdSense," was originally published at InfoWorld.com. Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest business technology news, follow InfoWorld.com on Twitter.