As Jamie Lynn Spears continues to promote her memoir 'Things I Should Have Said', questions about her relationship with sister Britney Spears have repeatedly come up.

In an interview on Good Morning America, Jamie Lynn Spears was asked about her sister's conservatorship, to which she answered: "When it was put into place I was 17 years old. I was about to have a baby, so I didn't understand what was happening."

She said she had "always been my sister's biggest supporter" and that it was up to her big sister to "walk through the door."

Jamie Lynn Spears also shared her memories of Britney's breakup with Justin Timberlake on the 'Call Her Daddy' podcast.

Britney has now issued a cease-and-desist letter via her attorney Mathew Rosengart.

In the letter obtained by People (via EW), Rosengart asks Jamie Lynn to stop sharing stories about his client's personal life while promoting her book.

The letter opens: "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.

"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."

It continues: "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.'"

It adds: "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."

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

In conclusion: "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.

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

Britney also responded to her Jamie Lynn Spears' latest interview in a lengthy Instagram post.