Gossip magazines have published topless pictures of Prince William's wife taken during a private holiday.
Travolta, who has faced unwelcome scrutiny of his own private life, told the BBC that it is the "worst time to be famous."
"There is a right to privacy whether you're famous or not famous, and I feel that anyone being invaded at that level is unfortunate and there should be a law, no one would like that," he said in an interview broadcast Friday.
Travolta plays a corrupt cop in Oliver Stone's drug-war film "Savages," which opens in Britain on Friday.
It's his first film since 2010. Recently he has been in the headlines for his private life, including a discredited - but widely reported - lawsuit claiming he had groped two masseurs.
Travolta, who has been one of Hollywood's best-known faces since he starred in "Saturday Night Fever" in 1977, said he almost retired from acting after the death of his 16-year-old son Jett in 2009.
He said that after his son's death from a seizure he'd "thought of retiring at one point because it felt like too much."
But he told the BBC that "after three years getting a lot of support from my church and a lot of support from people, fans, family I decided that it was OK to go back to work."
Travolta is a prominent member of the Church of Scientology.