John Travolta Sued By Book Author

The man behind the lawsuit is Robert Randolph -- who wrote a book in titled, "You'll Never Spa in This Town Again" ... detailing Travolta's alleged sexual exploits between John and other man, including Randolph.

In his suit, Randolph claims ... as he was releasing his book, Travolta and his high-powered attorney Marty Singer unleashed a P.R. attack ... in which they falsely claimed Randolph had mental issues and spent time in a mental institution.

Randolph claims the attack was concocted to persuade the public that he's an unreliable source ... and they should NOT buy his book. Randolph claims Travolta's plan worked ... and retailers were detoured from selling his book.