Like all states, California has licensed medical centers of every kind. One particular type, often known as a “crisis pregnancy center,” provide pregnancy‐related services with the goal of helping women to make choices other than abortion. Based on opposition to these centers, the California legislature enacted a law requiring licensed clinics “whose primary purpose is providing family planning or pregnancy‐related services” to deliver to each of their clients the following message: “California has public programs that provide immediate free or low‐cost access to comprehensive family planning services (including all FDA‐approved methods of contraception), prenatal care, and abortion for eligible women.” But the law also creates an exception for clinics that actually enroll clients in these programs — so, in effect, the law applies only to clinics that oppose the very program they must advertise. Several of these crisis pregnancy centers sued to block the law, arguing that it violated their First Amendment rights by forcing them to express a message to which they are opposed. But the U.S. court of Appeals for the Ninth Circuit upheld the law, holding that it regulates only “professional speech” and therefore should be reviewed under a more deferential standard, rather than the normal strict judicial scrutiny that applies to laws compelling speech. The centers have petitioned the Supreme Court to review their case; Cato has filed a brief supporting that petition. In our brief, we explain that the definition of “professional speech” that the Ninth Circuit applied is dangerously overbroad. Regulation of patient‐physician speech is justified by the notion that when doctors speak to their patients, they assume a special obligation to communicate their expertise fully and truthfully. These regulations protect patients, who can’t be expected to have the same specialized knowledge as their medical providers. But they can’t be extended beyond that bright line of specialized knowledge: if a state can force its doctors to read a pre‐written advertisement to their patients, it can force them to say anything the state wants. Compelling licensed professionals to speak the government’s message is dangerous for precisely the reasons compelled speech is always dangerous. Most importantly, it allows the government to impermissibly put its thumb on the scale in a social debate, by conscripting individuals to help spread a particular message. (Tellingly, California has no equivalent law forcing clinics to advertise adoption agencies or other choices.) Further, the law burdens the conscience of speakers, by forcing them to promote programs that they morally oppose. This is precisely the invasion of “the sphere of intellect and spirit” that Justice Robert Jackson warned of 70 years ago, in the first Supreme Court case to strike down a compelled‐speech law, West Virginia Board of Education v. Barnette (1943). The Court should grant review, reject the Ninth Circuit’s dangerous “professional speech” doctrine, and apply the lesson of Barnette in striking down this law.