From the article (bold added), more at link:

In September, Sen. Warren sent a letter to Amazon accusing it of peddling misinformation by promoting books spreading “falsehoods” about COVID-19. She said that the retailer’s algorithms had been recommending books promoting what she thinks is the wrong type of treatment.

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Warren’s letter singled out a book by Joseph Mercola and Ronnie Cummings, titled “The Truth About COVID-19: Exposing the Great Reset, Lockdowns, Vaccine Passports, and the New Normal.” According to Warren’s letter, Mercola had been described as “the most influential spreader of coronavirus misinformation online.”

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The publishers and authors of the book, along with Robert F Kennedy Jr, have jointly filed a complaint at the Western District of Washington court, accusing Warren of violating their free speech rights. Their complaint cites a past ruling in the Supreme Court in the Bantam Books v. Sullivan case, where state officials were found in violation of the First Amendment by sending letters to sellers warning them not to sell certain books.

Almost sixty years ago, in Bantam Books v. Sullivan, 372 U.S. 58 (1963), the Supreme Court held that state officials violated the First Amendment by sending letters to booksellers warning that the sale of certain named books was potentially unlawful.

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The “vice” in such letters and in the “veiled threat” of legal repercussions they communicated, explained the Court, is that they allow government to achieve censorship while doing an end-run around the judiciary, “provid[ing] no safeguards whatever against the suppression of . . . constitutionally protected” speech, thus effecting an unconstitutional “prior restraint.”

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The complainants also claim that Warren’s letter contained unsubstantiated accusations and falsehoods.

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“The term ‘vaccine misinformation,’ as Senator Warren uses it is propagandistic and false, referring to any speech challenging the safety and efficacy of the COVID vaccines, even when that speech consists of factually accurate information or reasonable and protected opinion,” the complaint states.

“Senator Warren broke the law and betrayed our fundamental right to free speech,” said Dr. Joseph Mercola, founder of Mercola.com, a natural health website. “No politician is above the law, I will do everything in my power to defend my constitutional rights as an American.”