On this day in 1918, the Sedition Act was passed by Congress forbidding Americans from using “disloyal, profane, scurrilous, or abusive language” about the U.S. government, flag, or armed forces during the ongoing First World War. It also allowed the Postmaster General to refuse to deliver any mail that, in his discretion, fit this description.
This was actually the second act of its name and kind, with the first being passed early in the history of the republic, in 1798 (though it expired in 1801). Those convicted under the 1918 act generally received prison sentences of five to 20 years.
The Sedition Act was actually a series of amendments to the Espionage Act passed the year before, which prohibited interference with the war effort, disruptions to military recruitment, or any attempt to aid an enemy nation (thus the two are properly spoken of as one law). It is estimated that there were around 1,500 prosecutions carried out under these acts, of which 1,000 resulted in convictions.
The most high profile case was that of Eugene V. Debs, the outspoken and influential leader of the Socialist Party, who had rallied against the war, in particular conscription; he was ultimately sentenced to ten years in prison, though his sentence was commuted to about three years.
Major media outlets at the time were either indifferent or outright supportive of the act, and the Supreme Court upheld its constitutionality in Abrams v. United States in 1919. As a wartime law, the act was ultimately repealed a couple years after the end of the First World War, although there was some support for passing a peacetime version (which ultimately happened with the Alien Registration Act of 1940, though that in turn was struck down by the Supreme Court in a series of cases in the 1950s).
Following the Court’s landmark ruling in Brandenburg v. Ohio (1969) — which gave broad leeway to “inflammatory speech” under certain conditions — it is believed that nothing like the Sedition Act could be passed again without being struck down as unconstitutional (though of course that remains to be seen).