The main attack on civil liberties in the US during WWI was the passage and enforcement of the Espionage and Sedition Acts. These acts made it illegal, in effect, to criticize government leaders and/or the war effort. It also allowed, for example, the postmaster-general of the US to bar anything from the mail that would violate the act. This law was used to imprison Eugene V. Debs for speaking out against the draft. The law was also used to obtain more than 1,000 convictions against people like Socialists.
Another possible candidate for an attack on civil liberties was the attack on all things German. For example, the teaching of German in public schools essentially disappeared during the war. This is, however, a less clear-cut case of infringement on civil liberties because there is no constitutional guarantee that any language can be taught in schools.
During times of war, the government has often limited the freedoms of its citizens. This was true in World War I. There were a few laws passed that limited our freedom. One of these was the Sedition Act. This law made it illegal to criticize the government and the war effort. The government was very concerned that if the Central Powers heard our people criticize the war, it would encourage them to keep fighting. We were worried the Central Powers would believe Americans would pressure our government to end the war.
Another law passed during the war that limited our freedoms was the Espionage Act. This law made it illegal for Americans to provide any form of help to our enemies. If somebody was convicted of this, they could be fined or jailed. The government took steps to try to keep opposition to the war at a minimum by passing these laws.
The Espionage and Sedition Acts were at the forefront of curbing civil liberties during World War I. The Espionage Act, 1917, was enacted shortly after the US joined the war and prohibited the insubordination of armed forces, targeting those who refused to serve and those who influenced them, thereby ensuring total control of liberties and uninterrupted military duties. Key political figure Eugene Debs, a three-time presidential candidate, was arrested and sentenced to prison. The Postmaster General ordered the censorship of mail to ensure the success of the government in its military campaign.
The Sedition Act of 1918 broadened the purview of the Espionage Act to prohibit speech and opinions that cast aspersion on the government's war efforts. Sentences of up to 20 years were provided to people arrested under this act.