Hit novels are often followed by lawsuits, as JK Rowling and Dan Brown can both testify. But the latest to be launched – against author Kathryn Stockett, whose novel The Help has been a major bestseller on both sides of the Atlantic, and will soon be a Hollywood film – is more unusual than most.

Stockett is not facing a charge of plagiarism brought by a less successful author, as both Rowling and Brown (who successfully defended their cases) did. Instead, she is being challenged by an woman, Ablene Cooper, who has worked for many years as a maid for Stockett's brother Robert.

The Help, as fans will know, is the story of African-American women working as maids in white families in the segregated south of the 1960s. A highly sympathetic portrayal of the women's experiences at the hands of their employers, its plot sees the maids find a way to speak out about the injustices and indignities they are usually forced to suffer in silence. One of the main characters is a wise and caring maid named Aibileen Clark.

Stockett, who grew up in the city of Jackson, Mississippi, where her brother still lives, has emphasised that her book is pure fiction but also talked of how the background is that of her own southern childhood, reflecting on her relationship with her family's maid, Demetrie, who died when she was a teenager.

Now 60-year-old Ablene Cooper has filed a lawsuit claiming that the character of Aibileen Clark is based on her, against her wishes, and asking for damages. Both Cooper and the fictional Clark had adult sons who died just before the birth of their white employer's first child, and both possess a gold tooth. The lawsuit says the fictional portrait is offensive to Cooper, citing in particular a passage where Aibileen compares her own black skin colour to that of a cockroach.

Stockett's UK publisher, Penguin, said the author had made no statement in relation to the case. Amy Einhorn, her US editor, commented: "This is a beautifully written work of fiction, and we don't think there is any basis to the legal claims. We cannot comment further regarding ongoing litigation."

The Help has spent 97 weeks so far on the New York Times bestseller list since its 2009 publication. A Dreamworks film, starring Viola Davis as Aibileen, is due for release in the summer.