In 2010, New York state prison inmate Mark Burns says he was stocking the commissary when a can of spaghetti sauce fell on his head. He says he duly reported the accident, but afterward, two guards approached him and said they'd heard he'd been assaulted by another inmate.

The guards had an offer, according to Burns: They wanted him to become an informant and provide false testimony against another guard. When he refused to play along, he was put in "involuntary protective custody." For nine months, he spent 23 out of every 24 hours locked in a cell by himself—"for his own safety." So Burns filed a federal civil rights lawsuit, claiming the guards violated his constitutional right not to snitch.

The Supreme Court has ruled on compelled speech in several landmark opinions, including West Virginia State Board of Education v. Barnette, which held that students may not be forced to salute the flag. Other cases have featured cops punished for refusing to cover up misconduct by fellow officers. But federal courts had never considered the right of inmates to refuse to become informants.

In an opinion issued this May, the 2nd Circuit Court of Appeals drew on a century of First Amendment jurisprudence to rule that the guards had engaged in unconstitutional retaliation against Burns.

"To force a person to speak, and compel participation, is a severe intrusion on the liberty and intellectual privacy of the individual," the court wrote. "Just as compelled silence will extinguish the individual's right of expression, compelled speech will vitiate the individual's decision either to express a perspective by means of silence, or to remain humbly absent from the arena."

The right to keep one's mouth shut, the decision continues, safeguards a "vitally important restraint on the government's coercive powers." The court even compared the guards' investigative methods to the hated "writs of general assistance" that British troops long ago used against American colonists.

That may sound like a resounding victory, but the ruling was actually a defeat for Burns. One sentence after declaring that he had been subjected to nine months of unconstitutional retaliation for exercising his right, the appeals court wrote that, because the right wasn't clearly established at the time, the guards who did it couldn't be sued, thanks to the doctrine of "qualified immunity."

Like so many First Amendment pioneers and jailhouse lawyers, Mark Burns carved out new protections for future inmates. Unfortunately, he will never see a cent from the officials who conspired against him under the color of law.