Britney Spears is threatening legal action against her sister, Jamie Lynn Spears, if she doesn't stop talking about her while promoting her new book, "Things I Should Have Said."

Through her attorney, Matthew S. Rosengart, the "...Baby One More Time" singer, 40, sent a cease-and-desist letter shared with ABC News and dated Jan. 17, to the "Zoey 101" alum, 30, stating that she will not be "exploited" for her sister's "monetary gain."

"...[T]he last thing Britney wants is to bring more attention to your ill-timed book and its misleading or outrageous claims about her," the letter began. "Although Britney has not read and does not intend to read your book, she and millions of her fans were shocked to see how you have exploited her for monetary gain. She will not tolerate it, nor should she."

Rosengart's letter also states the pop star was the "breadwinner" of the family and "also otherwise supported" Jamie Lynn before referring to the "abuse and wrongdoing" Britney has already been through.

"...[H]aving endured a 13-year conservatorship that stripped her of civil rights and fundamental liberties, Britney will no longer be bullied by her father or anyone else," the letter continued.

"She takes you at your word and we, therefore, demand that you cease and desist from referencing Britney derogatorily during your promotional campaign," the letter concluded. "If you fail to do so or defame her, Britney will be forced to consider and take all appropriate legal action."

ABC News reached out and there is no comment from Jamie Lynn Spears' team at this time.

This letter came two days after Britney tweeted that she loved Jamie Lynn and that her sister can "[s]ay whatever you want to say just know I do know your real heart more than anyone." The two had been sparring on social media following Jamie Lynn's tell-all interview with ABC News on Jan. 12.

VIDEO: Jamie Lynn Spears speaks out about memoir in 1st TV interview
Despite their complicated relationship, Jamie Lynn Spears tells Juju Chang she still has a deep love for her big sister, Britney Spears.

Jamie Lynn's personal memoir, "Things I Should Have Said," is out now.