Frank le Clavez is taking Disney and Pixar Films to court saying he wrote a book featuring fish characters long before the film came out.
He claims he was forced to take legal action when book shops in France stopping stocking his book, worried they might be sued by the film makers.
Disney denies the allegation, and the case will be heard by a court in Paris.
So far it's taken more than $670m (£385m) worldwide.
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