Barnes & Noble asked US regulators to investigate Microsoft on anti-trust grounds this summer, court documents have revealed.
Its submissions to the department accuse Microsoft of threatening Android vendors with litigation in order to stifle competition.
"Microsoft is embarking on a campaign of asserting trivial and outmoded patents against manufacturers of Android devices," Barnes & Noble wrote to the Justice Department in a letter seen by Bloomberg.
"Microsoft is attempting to raise its rivals’ costs in order to drive out competition and to deter innovation in mobile devices."
In March this year, Microsoft accused Barnes & Noble of infringing five user interface patents used in its Nook and Nook Color tablets, in a case due to be heard next February.
Barnes & Noble refused to license the patents, saying that to do so would impede its ability to provide software upgrades, and claiming that the fees Microsoft was seeking were excessive.
In its complaint, Barnes & Noble also raises the question of Microsoft's involvement in a group buying Novell patents, and of its licensing agreement with Nokia and Mosaid.
It descibes these moves as a series of tactics "designed by Microsoft to raise its rivals’ costs and prevent Android-based devices from taking away sales of Microsoft’s Windows operating system."
Microsoft's commented only to say that it makes its patents available on reasonable terms, and that Barnes & Noble is welcome to one if it likes. It's reached agreements with a number of other Android vendors.