The royal couple has already begun action against the French magazine Closer after it published a dozen shots of Catherine, Duchess of Cambridge - the former Kate Middleton - as she slipped off her bikini top while sunbathing at a French chateaux.
Both Chi and Closer are controlled by Italian publisher Mondadori, part of the media empire of former Prime Minister Silvio Berlusconi and chaired by his daughter Marina.
Chi Editor in Chief Alfonso Signorini said the special edition would include a 26-page reportage with topless pictures of the duchess, including some unpublished shots of her vacation with Prince William, second in line to the British throne.
"This reportage is worth a special edition. It shows in a very natural way the daily life of a young and famous couple very much in love," Signorini said in an emailed statement.
"The fact that we are dealing with the future British monarchs makes it certainly more interesting and in line with a modern conception of the monarchy," Signorini said.
Chi's front page, already widely published by Italian media, shows a large shot of Kate sitting topless, above the headline "Scandal at court: the Queen is Naked."
Prince William's office said there was no justification for further publication of the photos.
"We will not be commenting on potential legal action concerning the alleged intended publication of the photos in Italy save to say that all proportionate responses will be kept under review," his office said in a statement.
"Any such publication would serve no purpose other than to cause further, entirely unjustifiable upset to the Duke and Duchess of Cambridge, who were enjoying time alone together in the privacy of a relative's home."
Closer's pictures, already wildly circulating on the Internet, were also picked up by several foreign publications.
Greek newspaper Eleftheros Typos had two photographs of the duchess, one showing her topless, on its front page.
The pictures have reignited the debate over the privacy and freedom of the press, especially in Britain where the media face possible new regulations after a series of publishing scandals.
No British paper has published the photographs, including the Sun tabloid, the only British title to run pictures of William's brother Harry naked in a Las Vegas hotel.
"Her picture will be probably available online until the end of the earth. But it's not the end of the world," commentator Maria Laura Rodota wrote in Italy's biggest daily Corriere della Sera. (Reuters)