E-40 Warns Urban Novelist to Keep Away from 'Captain Save a Hoe'

E-40 says an author ripped off his hit '90s song and slapped it on a novel, but he's giving the writer one chance to save himself from a 'Save a Hoe' lawsuit.

The rapper fired off a cease and desist letter to novelist, CJ Allen over his book, "Captain Save A Hoe." In the letter, E-40 says he has a trademark on his 1993 track, which covers merch, services and, most importantly, publications ... like "novel books in the fields of urban fiction."

Forty Fonzarelli says Allen's book infringes on his song's copyrights and confuses fans. According to the docs, obtained by TMZ, a lawsuit will be filed if Allen doesn't scrap the novel and provide a full accounting of all money made off it.

We found out the author's currently in prison, but his wife doesn't think E-40 has a case. She tells us readers won't confuse the book's heroine -- a sexy woman in a cape with an "S" -- with the main character in 40's music vid, a guy in a shirt and cape with a "C."

She also claims the rapper's causing her husband financial harm and stress ... beyond the normal prison variety, we're guessing.