The French magazine that published topless pictures of the Duchess of Cambridge could be shut for up to five years and see the photographer who took the images imprisoned for up to a year.
The French version of the magazine 'Closer' published the images of Kate sunbathing while on a private holiday with husband William last September.
The publishing group Mondadori, which produces the magazine, is now being questioned by a Paris prosecutor.
Valerie Suau, a French photographer, is also under investigation along with her employer La Provence, a regional title, which printed photographs of the Duchess that did not involve nudity.
A spokesman for the prosecutor in the Paris suburb of Nanterre said: "The photographer and legal representatives of both companies have been questioned concerning the photographing of a person on private property and the criminal use of these images.
"The maximum penalty for this kind of offence is one year in prison and a fine of 45,000 euros (£38,350) for individuals.
"For corporate bodies, the fine is 45,000 euros, cessation of business for five years and public notification of the decision."
The development comes after the royal couple launched their own legal proceedings over the photos and a court in Paris banned Closer, a publication separate from the UK's Closer magazine. from publishing any further images.
Closer argued that the photos, taken while the couple holidayed in southern France at a chateau owned by Viscount Linley, the Queen's nephew, were shot from a public road.
William and Kate were angered by the intrusion into their privacy and the magazine and photographers involved were left in no doubt about their feelings when a strongly worded statement was issued by St James's Palace last year.
It said: "The incident is reminiscent of the worst excesses of the press and paparazzi during the life of Diana, Princess of Wales, and all the more upsetting to the Duke and Duchess for being so."
But pictures were also published in Italian gossip magazine Chi - Closer's sister magazine - and the Irish Daily Star, as the ruling did not cover publications outside France. No British newspapers printed them.
Mondadori, an Italian publishing group owned by former prime minister Silvio Berlusconi, said it was "not aware of anything new with respect to what is already known about the issue", while La Provence said Ms Suau had its "support in the legal challenge she is facing today", the BBC said.
A spokesman for St James's Palace said: "The ongoing legal process is a matter for the French authorities."