Britney Spears Sends Cease-and-Desist to Jamie Lynn Demanding She Stop with 'False,' 'Fantastical Grievances'

Britney Spears is asking her sister Jamie Lynn Spears to stop "derogatorily" referencing her while promoting her new book, Things I Should Have Said.

In a cease-and-desist letter obtained by PEOPLE, Mathew Rosengart, an attorney for Britney, 40, asked Jamie Lynn, 30, to stop sharing stories about his client's life in interviews on her book tour, which has included appearances on Good Morning America and the Call Her Daddy podcast.

"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," the letter begins. "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."

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Jason Merritt/Getty; Isaac Brekken/Getty

Rosengart continued, "You of all people know the abuse and wrongdoing Britney had to endure during the conservatorship, after initially growing up with a 'ruinous,' alcoholic father. In fact, your own book reportedly states that your father 'spent most of my life in that cycle of ruinous behavior. His bouts of drinking caused me periods of torment and sorrow.' "

"As I have previously stated, having 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," Rosengart wrote in the letter.

"Britney was the family's breadwinner and she also otherwise supported you," Rosengart continued. "Publicly airing false or fantastical grievances is wrong, especially when designed to sell books. It is also potentially unlawful and defamatory."

Rosengart then invoked a Michelle Obama quote, writing that Britney was going to follow the "when they go low, we go high" philosophy.

Phillip Faraone/FilmMagic; Michael Loccisano/Getty Images Britney Spears and Jamie Lynn Spears

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"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," he added. "If you fail to do so or defame her, Britney will be forced to consider and take all appropriate legal action."

The letter comes as Jamie Lynn and Britney have been publicly sparring on social media, with the sisters clashing over claims in Jamie Lynn's memoir.

Britney has accused her younger sister of trying to "sell a book at [her] expense" after Jamie Lynn has shared stories of her childhood in interviews, including claims that Britney behaved "erratically" at times and once locked the two of them in a room with a knife.

While appearing on Call Her Daddy Monday, Jamie Lynn shared memories of Britney's highly publicized breakup with Justin Timberlake. After the episode aired, Britney shared her own experience with the breakup in an Instagram post, writing that she "flew home to Jamie Lynn on the couch watching her tv shows right after Justin and I broke up" before comparing her own childhood to Jamie Lynn's.

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"I had worked my whole life," Britney wrote, adding, "meanwhile Jamie Lynn is 12, she indulges with the TV for hours then goes to lay out on a raft at the pool … I'm in shock because this was never my life !!!!"

Jamie Lynn has insisted she supports and loves Britney, and issued a public plea to stop their feud on her Instagram Story on Saturday.

"Britney- Just call me, I have attempted many times to speak to you directly and handle this privately like sisters should, but you still choose to do everything on a public platform," she wrote at the time, PEOPLE previously reported.

Jamie Lynn added, "In the meantime, please stop continuing the narrative that I haven't been there for you or that I'm making things up. I'm happy to share how many times I've reached out to you, supported you and tried to help you. This is embarrassing and has to stop. I love you."