A federal appellate court has blocked enforcement of a California law that requires large social media platforms to disclose their editorial policies -- including how they treat hate speech and other objectionable material.

In a decision issued Wednesday, a three-judge panel of the 9th Circuit Court of Appeals ruled that the law (AB 587) likely violates the First Amendment by compelling companies to speak about controversial matters.

AB 587, signed last year, requires large social media platforms to post information about their content moderation policies, and provide semiannual reports to the state attorney general about enforcement. Those reports are supposed to include information about whether and how the companies define and handle certain categories of objectionable material -- including hate speech, extremism and disinformation.

The law also allows the attorney general to seek penalties of up to $15,000 a day from a platform that “materially omits or misrepresents” its policies.

X (formerly Twitter) sued to block the law last year, arguing that the statute interferes with editorial judgments about how to treat users' speech. The company contended that even though the state touts the law as a “transparency” measure, the legislature intended to pressure platforms to suppress constitutionally protected speech.

In general, the First Amendment protects all lawful speech -- including material considered hate speech and disinformation.

Late last year, U.S. District Court Judge William Shubb in Sacramento rejected X's request to block enforcement. He wrote that even though the law appears to place a “substantial burden” on social media companies, it wasn't “unjustified or unduly burdensome within the context of First Amendment law.”

X then appealed to the 9th Circuit, arguing that the law forces it “to engage in controversial speech against its will.”

Attorney General Rob Bonta countered that the statute is merely a transparency measure, and that the matters that companies must disclose are “purely factual and uncontroversial.”

The appellate panel sided with X, writing that the law's requirements are “not narrowly tailored” to the goal of transparency.

“Consumers would still be meaningfully informed if, for example, a company disclosed whether it was moderating certain categories of speech without having to define those categories in a public report,” Circuit Judge Milan Smith, Jr. wrote in an opinion joined by Mark Bennett and Anthony Johnstone. “Or, perhaps, a company could be compelled to disclose a sample of posts that have been removed without requiring the company to explain why or on what grounds,” Smith added.