Barnes & Noble is asking the US Department of Justice (DOJ) to investigate Microsoft for antitrust violations, alleging that the software giant is unfairly threatening companies that license the Android mobile OS. The last major US retail bookseller, Barnes & Nobile uses Android in its popular Nook e-reader and tablet devices.

"Microsoft is embarking on a campaign of asserting trivial and outmoded patents against manufacturers of Android devices," Barnes & Noble wrote in a letter to the DOJ. "Microsoft is attempting to raise its rivals' costs in order to drive out competition and to deter innovation in mobile devices."

The Barnes & Noble complaint is interesting on a number of levels. Microsoft has been busy threatening the companies that use Android in their devices, alleging that the OS infringes on dozens of its patents. But most of these companies have simply entered into costly cross-licensing agreements with Microsoft rather than test that theory in court. And Microsoft revealed in late October that companies accounting for more than half of all Android devices have now entered into patent-license agreements with Microsoft.

Barnes & Noble is not one of those companies, and it stands aside a small group of holdouts that include Foxconn and Inventec. And Barnes & Noble has been unusually loud and public about its complaints. The firm has sent four formal complaints about Microsoft to the DOJ this year alone and has released each to the public.

According to Barnes & Noble, Microsoft and other companies—including Apple and Nokia—are engaging in patent litigation specifically to keep competitors' costs high and artificially harm their chances of succeeding. A lawyer for the firm says that these companies use "a series of tactics ... to raise rivals' costs and prevent Android-based devices from taking away sales" of their own platforms.

Microsoft says this activity is nothing new, and of course the software giant previously threatened companies that used Linux, another free OS that Microsoft says infringed on its patents. Microsoft was previously able to corral numerous Linux resellers into cross-licensing agreements as well.

"All modern operating systems include many patented technologies," a Microsoft statement reads. "Microsoft has taken licenses to patents for Windows and we make our patents available on reasonable terms for other operating systems, like Android. We would be pleased to extend a license to Barnes & Noble."

But Barnes & Noble is also unique in that it is poised to defend its position in court. A trial pitting Microsoft's patent claims against Barnes & Noble is set to begin in February. It will be interesting to see whether this trial actually occurs. Barnes & Noble's numerous complaints to the DOJ suggest that the firm would like this issue to simply go away.