Massachusetts Sen. Elizabeth Warren (D) used “strong rhetoric” when writing to Amazon about the anti-vaccine book “The Truth About COVID-19,” but didn’t violate the First Amendment by crossing the line from attempted persuasion to coercion, a federal appellate court ruled Thursday.

The ruling, issued by a three-judge panel of the 9th Circuit Court of Appeals, upholds a trial judge’s refusal to order Warren to retract the letter.

The decision comes in a battle between Warren and anti-vaccine activist Robert F. Kennedy, Jr.

Their dispute dates to September 2021, when Warren said in a letter to Amazon CEO Andy Jassy that the company was contributing to the spread of false information about the pandemic by promoting the book, writing that it “perpetuates dangerous conspiracies about COVID-19 and false and misleading information about vaccines.”

Kennedy, who last month announced a bid for the 2024 Democratic presidential nomination, was banned from Instagram in February 2021 for, according to the company, “repeatedly sharing debunked claims about the coronavirus or vaccines.” 

Soon after Warren sent the letter to Jassy, the book’s authors and publisher, as well as Kennedy, who wrote its forward, alleged in a lawsuit that the lawmaker violated the First Amendment by complaining about the book to Jassy.

Kennedy and the others sought an injunction that would have required Warren to retract her letter.

U.S. District Court Judge Barbara Rothstein in Seattle rejected that request, following which the plaintiffs appealed to the 9th Circuit.

On Thursday, that court upheld Rothstein’s decision.

“The plaintiffs have not raised a serious question as to whether Senator Warren’s letter constituted an unlawful threat in violation of the First Amendment,” Circuit Judge Paul Watford wrote in an opinion joined by Michelle Friedland. “Her letter requested, but did not demand, that Amazon reevaluate its business practices regarding COVID-19 misinformation and report back any changes. The absence of a specific demand is unsurprising, given that Senator Warren lacks direct regulatory authority over Amazon in this matter.”

In her letter to Jassy. Warren said that the top search result on Amazon for the terms “COVID-19” and “vaccine” was “The Truth About COVID-19,” and asked him to review Amazon’s algorithms, report on whether they recommended books with incorrect information about COVID-19 and, if so, develop a plan to modify them.

The senator also noted that she had earlier raised concerns regarding “false and misleading” information about KN95 masks, adding: “This pattern and practice of misbehavior suggests that Amazon is either unwilling or unable to modify its business practices to prevent the spread of falsehoods or the sale of inappropriate products — an unethical, unacceptable, and potentially unlawful course of action from one of the nation’s largest retailers.”

Kennedy and the others argued to the 9th Circuit that Warren’s letter could be viewed as a threat, particularly because she called Amazon’s activity “potentially unlawful.”

The appellate judges rejected that argument, writing that Warren used “strong rhetoric,” but didn’t violate free-speech principles.

“Generating public pressure to motivate others to change their behavior is a core part of public discourse,” Watford wrote.

He added that her use of the phrase “potentially unlawful” didn’t cross the line into attempted censorship.

“Placed in proper perspective, the phrase ‘potentially unlawful’ most likely refers to the ‘sale of inappropriate products,’ such as the unauthorized KN95 masks,” he wrote. “Such a business practice could potentially constitute unlawful consumer fraud… Even if we accept the plaintiffs’ reading of the letter, however, referencing potential legal liability does not morph an effort to persuade into an attempt to coerce.”

Circuit Judge Mark Bennett concurred with the decision to uphold Rothstein’s, but argued that some parts of Warren’s letter “could be interpreted as coercive by a reasonable reader.”

Sen. Elizabeth Warren did not use coercion when objecting to Amazon about an anti-vax book, a judge ruled, writing: “Public pressure to motivate others to change their behavior is a core part of public discourse.”