Spears' lawyer, Mathew Rosengart, on Tuesday sent a legal termination letter to the singer's younger sister regarding her new memoir, "Things I Should Have Said".
In Rosengart's letter, he calls the book "poorly timed" and that it makes "misleading or outrageous allegations about her."
Although Jamie Lynn Spears recently said that the book is not about her sister, Rosengart wrote: "She takes you at her word and we therefore demand that you stop and refrain from mentioning Britney derogatoryly during your promotional campaign. If if you fail to do so or defame her, Britney will be forced to consider and take all appropriate legal action. "
In her book, she describes her sister's behavior as she grew up at times as "paranoid" and "irregular".
In a recent interview while promoting her book on "Good Morning America," Jamie Lynn Spears said, "I've always been my sister's greatest support."
She also said she had nothing to do with her sister's 13-year-old conservatory, which was completed late last year.
"When she needed help, I established ways to do it, went out of my way to make sure she had the contacts she needed, to possibly go ahead and quit this conservatory and just quit it all. "If it's going to cause so much discord, why go on with it? I even talked to her legal team, ... her former legal team, and it did not end well in my favor." Addition: "I took the steps to help. How many times can I take the steps without ... She has to go through the door."
CNN has contacted Jamie Lynn for comment on the legal letter.