Britney Spears' relationship with her sister Jamie Lynn has deteriorated. In anticipation of her sister's memoir being released on January 18, actress Zoey 101 has given several interviews in which she mentions Britney.

Britney released an open letter on Twitter, and Jamie Lynn is reportedly skipping the book tour.

But that is not satisfactory to Britney and her attorney Matthew Rosengart, who wrote a cease and desist letter to Jamie Lynn, obtained by E.News, which was written by the latter.

"The last thing Britney needs is to bring further attention to your ill-timed book or misleading or outrageous claims about her.

Rosengart continued, "You are aware of the abuse and misconduct that Britney had to endure during her conservatorship after growing up with a 'catastrophic' alcoholic father. In fact, in your own book, your father wrote: 'I spent most of my life in a cycle of catastrophic behavior. His bouts of drinking brought me periods of anguish and grief.'

Getting to the heart of the matter, the letter states. "Publicizing false or fanciful complaints, especially when made to sell books, is wrong. It is also potentially illegal and defamatory.

The intent of the letter was in response to Jamie Lynn's previous claim that the book was not about Britney, stating, ". If it does not, or if it defames her, Britney will be forced to consider and take all appropriate legal action."

While behavior such as one sister threatening to sue the other is not indicative of an ideal family relationship, entertainment attorney Mitra Ahourian said that Britney and her legal representatives could, if they wanted to (which implies that they probably did not want indicate), they could have made it tougher.

"Matthew Rosengart's letter is more like a plea than a threat," Ahourian told Marie Claire.

"It says that Jamie Lynn Spears' decision to air her grievances in public is 'wrong,' but this is more of a moral than a legal argument. And Jamie Lynn Spears' statement is potentially illegal and defamatory, and Britney may have to consider taking legal action, as opposed to stating explicitly that the statement is defamatory, with only qualifiers that temper the language.

Other than simple family loyalty, one reason Starr does not want to actually sue Jamie Lynn is that it is not an easy case.

"Britney Spears is in a tough position because as a public figure, the hurdles to prove defamation in court are very high," explains Ahourian. 'For a private person to be found guilty of defamation, the statement simply has to be true. But for Britney, a celebrity, to prove that Jamie Lynn defamed her, she must prove that Jamie Lynn made those statements with actual malice.

"Here, Britney, through her attorney, suggests that Jamie Lynn's statements are false. If proven false, her attorney has established through this letter that Jamie Lynn either knew about them or ignored the possibility that the statements were false and continued to make them. This letter would help establish the malice necessary for a celebrity to bring a defamation action. But that is only the first step. Britney Spears and her lawyers still face the hurdle of proving that Jamie Lynn's statements are untrue."

Ahourian adds that the letter's visibility is important with regard to Britney's fans.

"This letter is meant to gain public sympathy. This letter gives us another way to counter the narrative that is damaging to Britney Spears' public image." Rosengart offered a statement more eloquent than anything Britney has ever posted on Twitter or Instagram, knowing that it would be widely quoted in the media."