It is alleged that Ms Rowling copied a large part of Jacobs's story The Adventures of Willy the Wizard and had it published as her own work in Harry Potter and the Goblet of Fire.
Bloomsbury say the allegation is "unfounded and untrue" and Rowling has, as yet, made no comment on the matter.
DMH Stallard, representing the estate of Adrian Jacobs, confirmed that legal action was being taken against Bloomsbury Publishing for copyright infringement.
Jacobs died in London in 1997 and the book in question that Rowling is said to have copied was published in 1987.
Bloomsbury admit that Jacobs's estate first approached the company back in 2004 but they were unable to find any text in Ms Rowling's work that looked as if it was copied from the other writer.
