So reports Ars Technica, and points to the complaint.
The complaint is based on breach of contract, a violation of the Computer Fraud and Abuse Act, trespass to chattels, conversion, and a violation of the Washington Consumer Protection Act. As I noted earlier, Amazon's actions were indeed not authorized under the terms of use, which say that "Amazon grants you the non-exclusive right to keep a permanent copy of the applicable Digital Content and to view, use, and display such Digital Content an unlimited number of times." This makes for a strong breach of contract claim (though the damages might well be modest), and makes the other claims at least plausible, though I don't know enough to speak in detail about them. I also can't speak to whether class certification would indeed be sound here.
Special note: Two of the proposed classes for class certification purposes are labeled "The Big Brother Class" and "The Big Brother Work-Product Subclass." Shades of the anonymous plaintiff Guy Montag Doe?
By the way, according to the Complaint, "Earlier in 2009, Amazon reportedly remotely deleted certain copies of "Harry Potter" books by J.K. Rowling and certain copies of books by Ayn Rand." Assignment: Discuss, in light of Howard Roark blowing up the housing project.