Apple and two publishers are preparing to fight the Justice Department in court if necessary over pricing agreements for digital books, said two people with knowledge of the matter.

Apple, Pearson’s Penguin Group, and Macmillan, a unit of Verlagsgruppe Georg von Holtzbrinck, want to protect the “agency model” that lets publishers — not vendors — set e-book prices, said the people, who declined to be identified because they weren’t authorized to speak publicly.