The feud between pop monolith Britney Spears and her younger sister, actor and country singer Jamie Lynn Spears, continues to heat up. According to documents obtained by People, the elder Spears has filed a cease-and-desist letter to prevent Jamie Lynn from sharing anecdotes about Britney as she promotes her new memoir, Things I Should Have Said.

Among the stories Jamie Lynn has shared in interviews are her claim that Britney once locked the two of them in a room with a knife, and other statements about her older sister's "erratic" behavior over the years.

But Britney argues that Jamie Lynn is exploiting her to pad book sales, especially because Things I Should Have Said arrives just a few months after Britney's 13-year conservatorship was overturned in November, after a massive social media push, "Free Britney" rallying and renewed fan interest.

"We write with some hesitation because the last thing Britney wants is to bring more attention to your ill-timed book and its misleading or outrageous claims about her," writes Britney's attorney, Michael Rosengart, in the cease-and-desist letter. "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."

The letter underscores the "abuse and wrongdoing" endured by Britney at the hands of her father, pointing out that the hardship the two sisters endured in their family is in fact a plot point in Jamie Lynn's memoir. Given that, "Britney will no longer be bullied by her father or anyone else," it continues.

"You recently reportedly stated that the book was 'not about her.' 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 culminates. "If you fail to do so or defame her, Britney will be forced to consider and take all appropriate legal action."

The letter comes amid a social media feud between the two sisters, with each lobbying lengthy social media posts at the other. Britney asserted that Jamie Lynn was planning "to sell a book at my expense," and the younger Spears fired back with criticism for Britney's "vague and accusatory posts."

Still, both have — thus far — maintained that ultimately, they support one another. "Britney — just call me, I have attempted many times to speak to you directly and handle this privately like sisters should," Jamie Lynn wrote in an Instagram Story (quote via People.)

On Twitter, Britney wrote that she loves her younger sister "unconditionally," and told her that "I know you worked hard for the life you have and you have done amazing." She added that it was "so tacky" for a family to fight publicly, but maintains that "you say you love me ... yet your loyalty is still with the people that hurt me the most!!!"

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