(CNN) The public feud between Britney Spears and her sister Jamie Lynn Spears is far from over.
Spears' lawyer, Mathew Rosengart, sent a legal cease-and-desist letter to the singer's younger sister on Tuesday regarding her new memoir, "Things I Should Have Said."
In Rosengart's letter, he calls the book "ill-timed" and that it makes "misleading or outrageous claims about her."
Although Jamie Lynn Spears has recently said that the book is not about her sister, Rosengart wrote, "She takes you at your word and we, therefore, demand that you cease and desist from referencing Britney derogatorily during your promotional campaign. 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 growing up at times as "paranoid" and "erratic."
But the Grammy winner has taken to social media multiple times over the last week to take issue with her sister's recollection. Writing on Instagram this week, "Jamie Lynn, I wasn't strong enough to do what should have been done ... slapped you and Mamma right across your f***ing faces !!!!!"
In a recent interview while promoting her book on "Good Morning America," Jamie Lynn Spears said, "I've always been my sister's biggest supporter."
She also said that she had nothing to do with her sister's 13-year conservatorship, which was terminated late last year.
"When she needed help, I set up ways to do so, went out of my way to make sure that she had the contacts she needed to possibly go ahead and end this conservatorship and just end this all for our family. If it's going to cause this much discord, why continue it? I even spoke to her legal team, ... her previous legal team, and that did not end well in my favor." Adding, "I did take the steps to help. How many times can I take the steps without ... She has to walk through the door."
CNN has reached out to Jamie Lynn for comment on the legal letter.