Earlier this year we told you about how Amazon was quietly working with Twitter, giving customers a button to tweet Amazon product pages with a short "amzn" URL. Now Amazon is more directly harnessing Twitter for online sales. The company today gave its affiliates a way to tweet products and get a cut of any sales that result from people clicking on the link. Amazon's move to turn Twitter into a sales referral machine, however, is raising fears that the ecommerce giant will flood Twitter with hidden advertising.

Amazon affiliates earn money by putting Amazon links and banner ads on their websites and collecting referral fees when people click on those links/ads and buy something. Now they'll have the option of tapping Twitter for those fees as well. Here's how it works: affiliates go to an Amazon product page, hit the "Share on Twitter" button on their tool bar, and get an auto-generated message on their Twitter account with a short product URL and their affiliate ID. They can edit the message, or just hit update to post it. If Twitter users click on the link and make a purchase, the affiliate gets a fee.

Amazon has an interesting relationship with Twitter. Amazon CEO Jeff Bezos is a personal investor in the microblogging service, and Twitter uses Amazon's S3 cloud service for storing profile and background pictures. Various Amazon business units use Twitter to build buzz around products and services, but now Amazon seems to be making a more serious effort to leverage Twitter for ecommerce.

Some are already questioning Amazon's new embrace of Twitter, saying it could pollute Twitter with more spam. From ReadWriteWeb:

This is the internet's version of "product placement" - subtle advertising in plain sight yet never clearly identified as such. Was your favorite TV star using a Macbook? Was he drinking a Coke? Already commonplace in Hollywood, these almost subliminal advertising messages permeate our consciousness every time we turn on the TV. Now that same sort of hidden ad will soon show up in the Twitter streams of your favorite tweeters.

Amazon is asking people to give feedback on Twitter with the hashtag #AMZNSOT.