Congress responded to a growing fear that public criticism of the war effort would make it difficult to conscript the needed manpower for American participation. Also contributing to widespread unease were the actions of labor groups, especially the Industrial Workers of the World (IWW), who proclaimed their sympathy for laborers through the world, including those in Russia.
The Espionage Act, passed in June 1917, provided penalties of 20 years imprisonment and fines up to $10,000 for those convicted of interfering with military recruitment.
The law also authorized the Postmaster General to remove treasonable or seditious material from the mail.
This measure was quickly challenged in the courts. In a controversial Supreme Court decision, Schenck v. United States (1919), the law was upheld. Congress had the power to enact legislation that under ordinary circumstances might not be acceptable, when faced by a clear and present danger. The terms of the Espionage Act were strengthened by the enactment of amending legislation, the Sedition Act of 1918.
State and local Committees of Public Safety, although they often did effective work, also at times exceeded legitimate object and left a memory of unjust repression in some communities. No formal censorship existed but the result was the same, through pressure and the mere threat of prosecution under the Espionage Act of 1917.