Injunctions against committing libel are one of the important exceptions to the general principle that the government cannot restrain your speech ahead of time, as distinct from prescribing legal consequences that might apply to it afterward. Eugene Volokh is serializing at Volokh Conspiracy some of the main points of a new article he has published in the Penn Law Review that draws a close connection between anti-libel injunctions and another anomaly of speech regulation, criminal libel (which departs from the general modern rule that legal consequences for unjust harm to reputation are generally civil and compensatory). He writes:
An injunction against libel, which carries the threat of prosecution for criminal contempt, is like a miniature criminal libel law—just for a particular defendant, and just for statements about a particular plaintiff. That is its virtue. That is its danger. And that is the key to identifying how the First Amendment and equitable principles should constrain such injunctions.
Injunctions themselves can be divided between permanent injunctions entered after a civil trial on the merits has found earlier speech to be libelous, and preliminary injunctions entered before there exists such a record. The two types of remedy have different potential dangers. The criminal libel comparison makes clear some of the other problems that can arise with libel injunctions, which include overbreadth and the lack of an equivalent of prosecutorial discretion.