Harry Potter author J.K. Rowling arrived at a New York courthouse on Monday to begin her battle with a fan hoping to release an encyclopedia about the fantasy series.

Rowling claims Steven Vander Ark's Harry Potter Lexicon is a "rip-off" and infringes on a number of her trademarks.

She has so far managed to stall the publication of the 400-page text - initially intended for release last November - and hopes her latest day in court will result in it being scrapped altogether. In a declaration filed in the U.S. District Court in February, Rowling said she was "very frustrated that a former fan has tried to co-opt my work for financial gain.

"I feel intensely protective, firstly, of the literary world I spent so long creating, and secondly, of the fans who bought my books in such large numbers."

Rowling has also revealed she plans to write her own Potter Encyclopedia.

Vander Ark's publishers RDR Books insist the book would promote the sale of Rowling's work - and accuse her of appearing to claim "a monopoly on the right to publish literary reference guides, and other nonacademic research, relating to her own fiction".

A spokesperson adds, "This is a right no court has ever recognized. If accepted, it would dramatically extend the reach of copyright protection and eliminate an entire genre of literary supplements."