Campbell Black, the author of thrillers such as Jig and Mambo, is suing over unpaid fees for writing the novel based on the smash-hit film Raiders of the Lost Ark, which starred Harrison Ford as Indiana Jones.
The book was a global bestseller, but despite its success Mr Lucas, whose company, LucasFilm, produced the 1981 movie and contracted Mr Black to write the novel, has never revealed how many copies were sold and how much money is now owed to the author.
Mr Black has accused LucasFilm of providing him with incomplete, inaccurate and deceptive information, and on Monday he will attend a court-ordered mediation process in San Francisco, where the billionaire film director is based.
The author, who writes under the name Campbell Armstrong, said yesterday: "All of LucasFilm's secrecy and misinformation in this matter is truly shabby. There is something seriously wrong with it. This is not about money. It's about justice. I don't want George's money, but I surely do want mine."
The lawsuit against LucasFilm has also accused the company of fraud as Mr Black's lawyers believe it deliberately attempted to deceive him about sales. His lawyer, Morris Getzels, said: "It has become abundantly clear that the studio never intended to pay Campbell more than his advance and intentionally concealed that fact from him - entitling him to punitive damages."
In 1980, Mr Black, who was then living in the US, was asked to transfer the screenplay of Raiders of the Lost Ark, which was directed by Steven Spielberg, into a full-length novel. The contract stipulated that he would be paid $35,000 (19,229), plus 2 per cent of domestic American sales and 1 per cent of foreign sales. While Mr Black was paid his advance, he never received additional payment for sales.
Over the years, his previous agents said that the novel had not sold enough copies to earn any money beyond the advance, which was surprising as the book was picked as a "book of the month club" selection by one large retailer.
However, in 2003 Mr Black joined Contemporary Talent Partners, an agency run by Anita Haeggstrom in Los Angeles, and she decided to press LucasFilm for up-to-date sales statements, which she said did not add up.
Ms Haeggstrom said: "We had our accountant examine the statements Lucas finally sent us last year and he found elements of them to be highly suspicious." After LucasFilm made a final settlement offer of just $450, Mr Black decided to take legal action. David Givens, the lawyer representing LucasFilm, was unavailable for comment last night.