There's an interesting article in today's NYTimes on this topic. From the article:
On Friday, Markus Dohle, chief executive of Random House, sent a letter to dozens of literary agents, writing that the company’s older agreements gave it “the exclusive right to publish in electronic book publishing formats.”
Backlist titles, which continue to be reprinted long after their initial release, are crucial to publishing houses because of their promise of lucrative revenue year after year. But authors and agents are particularly concerned that traditional publishers are not offering sufficient royalties on e-book editions, which they point out are cheaper for publishers to produce. Some are considering taking their digital rights elsewhere, which could deal a financial blow to the hobbled publishing industry.