The posters featured images of white actors Michael Fassbender and Brad Pitt more heavily than that of black actor Chiwetel Ejiofor, who played the main character of the film, the BBC reported.
BiM apologized for the "inappropriate" posters.
"We are very proud of the film and regret any distraction this incident may have caused," a statement from BiM said. "We apologize for creating and releasing unauthorized posters for '12 Years A Slave' in Italy featuring Brad Pitt and Michael Fassbender in a manner inconsistent with approved advertising materials.
"All inappropriate materials have now been withdrawn," the statement added.
The film's sales agent, Lionsgate's Summit, said the posters had not been authorized by producers.
Summit was "investigating and taking immediate action to stop the distribution of any unauthorized posters and to have those posters currently in the marketplace recalled," a statement from the company said.
The film features Ejiofor as a New Yorker who is abducted and sold into slavery in 1841.