On First Amendment grounds, a federal appeals court on Tuesday blocked enforcement of an Illinois law that makes it a felony to take video - with sound -- of police officers on the job.

The U.S. 7th Circuit Court of Appeals sided with the American Civil Liberties Union in challenging the Illinois eavesdropping law.

Judge Diane Sykes wrote for the 2-1 majority. Judge Richard Posner dissented, suggesting the hot-button issue could get a rehearing by the full court, or ultimately make its way to the U.S. Supreme Court.

From the Sykes' opinion:

The Illinois eavesdropping statute restricts a medium of expression commonly used for the preservation and communication of information and ideas, thus triggering First Amendment scrutiny. Illinois has criminalized the nonconsensual recording of most any oral communication, including recordings of public officials doing the public’s business in public and regardless of whether the recording is open or surreptitious.

Defending the broad sweep of this statute, the State’s Attorney relies on the government’s interest in protecting conversational privacy, but that interest is not implicated when police officers are performing their duties in public places and engaging in public communications audible to persons who witness the events.

Even under the more lenient intermediate standard of scrutiny applicable to content neutral burdens on speech, this application of the statute very likely flunks. The Illinois eavesdropping statute restricts far more speech than necessary to protect legitimate privacy interests; as applied to the facts alleged here, it likely violates the First Amendment’s free speech and free-press guarantees.

The ACLU planned to openly record Chicago-area police performing their duties in public places as part of an accountability project, and sought a declaratory judgment ahead of time. A judge initially dismissed the suit for lack of standing. The ACLU filed an amended complaint that sufficiently alleged a threat of prosecution against its videographers, but the court found that there is no First Amendment right to record audio, and again dismissed. The ACLU appealed.

The majority calls the Illinois eavesdropping statute a "national outlier," because it appears to be the broadest such law in the nation. Most others, the court notes, are concerned with protecting private conversation, not that of police conducting official business in public, or to surreptitious recording, not the kind done openly and observable by those being recorded.

In his 13-page dissent, Posner said invalidating statutes on constitutional grounds should be "a rare and solemn judicial act" and that the majority's opinion "casts a shadow" over other states' electronic privacy laws.

Posner lists several kinds of conversations someone might be having with a police officer on the street, that the person would not want recorded and put out on the internet or the evening news.

:Privacy is a social value," Posner wrote. "And so, of course, is public safety." He suggests both are endangered by the majority's ruling.

"A fine line separates “mere” recording of a police-citizen encounter (whether friendly or hostile) from obstructing police operations by distracting the officers and upsetting the citizens they are speaking with."

Posner observes that lots of private conversations occur in public places, in part because those talking assume that anonymity and the limited memory of those who might hear would limit the risk of publication.