Ben Domenech, publisher of the online politics and culture website The Federalist, jokingly tweeted from his personal Twitter account: “FYI @fdrlst first one of you tries to unionize I swear I’ll send you back to the salt mine.” Another Twitter user with no connection to The Federalist filed a charge with the National Labor Relations Board (NLRB), claiming the tweet amounted to an unfair labor practice by parent company FDRLST Media: threatening reprisal against those wishing to form a union.

The NLRB administrative law judge agreed, as did the Board, ordering Domenech to delete the tweet, among other relief. That order has now been appealed to the U.S. Court of Appeals for the Third Circuit.

Cato has filed a brief supporting FDRLST Media, joined by a broad coalition of free speech advocates including satirist P.J. O’Rourke, former ACLU president Nadine Strossen, and magicians and authors Penn & Teller. The brief explains that the NLRB was wrong for a simple reason: Domenech’s tweet was a joke, not a threat.

As the brief explains, both text and context show that the tweet was not a serious threat. Domenech uses his Twitter account to comment (often irreverently) on current events, and that context matters. A public tweet is different from a private email, just as a public speech is different from a private conversation. Domenech wrote the tweet to address and entertain his thousands of Twitter followers, not to privately threaten The Federalist’s six employees.

Even putting that context aside, The Federalist obviously does not have a salt mine to which insolent writers are banished. The absurdity of that suggestion is what makes the tweet funny, and that’s why The Federalist’s own employees understood that it was a joke.

But as our brief explains further, even though the tweet was a joke, this case is not. If you can be haled into court and found in violation of federal law on the basis of satire, sarcasm, or hyperbole, everyone will self‐​censor their humor, to the detriment of freewheeling discourse.

Will the NLRB next come for motivational posters saying, “the beatings will continue until morale improves”? Will exasperated exhortations on Twitter to “burn it all down” lead to house calls from the FBI? Better not to start down that path.

The NLRB should learn to take a joke, and the Third Circuit should decline to enforce the NLRB’s order.