Amazon MP3 Store has a promotion called Daily Deal, where they prominently highlight an album that'll rake in sales for cheap—in exchange, labels have been giving them a one-day exclusive before the street date. Surprise, iTunes got pissed.
For example, Amazon sold Mariah Carey's "Memoirs of an Imperfect Angel" for $6 and Vampire Weekend's "Contra" for $4, both a day before the street date in a Daily Deal promo. So, after telling labels it wasn't the wisest move to give Amazon any kind of exclusive window over iTunes, iTunes has apparently been pulling marketing support for music featured in Amazon's Daily Deals. Acording to Billboard, record labels Capitol and Jive backed out of Amazon Daily Deal promos they were considering for artists like Ke$ha, and Hollywood Records turned down Amazon's offer entirely to do a Daily Deal on Nick Jonas' new album, as result.
Amazon and Apple have been fighting it out over music for years—Amazon beat iTunes to being DRM-free, largely because labels feared iTunes' massive influence over the industry, given the iPod's 70 percent marketshare. So, they hoped to build up a credible threat in Amazon (which is why it's not entirely surprising to see them still give Amazon some favorable treatment, since it's essentially the MP3 store the labels built). Now with books in the content mix, it's even more tense. Though when it comes to publishing, the shoe's on the other foot: The publishers are flocking to Apple because they're afraid of Amazon, who commands between 80 and 90 percent of the ebook market.