I was wondering when this would happen.
Ever since the 5 publishers settled the antitrust lawsuit brought against them by the DOJ in 2012 I had been waiting for ebook retailers to file a similar lawsuit. The DOJ settlement only dealt with restitution for consumers that were forced to pay a higher price for ebooks, but they weren't the only affected party.
Agency Pricing enabled publishers to control the retail prices of the ebooks they published, and that control restricted ebookstores from competing by selling the ebooks at a cheaper price. In short, Diesel eBooks is arguing that Agency artificially restrained the ability of Diesel eBooks to compete in the market.
Would anyone care to make a bet as to how long it will take before the publishers settle? Given that they have already tacitly admitted to the conspiracy when they settled with the DOJ, any defense they might mount in this case will be weak. I would like to say that they have no defense, but that doesn't mean they cannot stall the case with motions, appeals, and other tricks. They might even be able to win on a technicality.
Apple, on the other hand, is probably going to fight this case as vigorously as they are continuing to appeal the antitrust lawsuit brought by the DOJ. Apple may have lost that case, but they are continuing to fight it on appeal. And they might win, too.