This question refers to the leaflet created by the Socialist Party of America (headed by Charles Schenck) which opposed the United States' entry into the war. The purpose of the leaflet was to convince people to resist the draft.
The leaflet had two sides. One read "“Long Live The Constitution Of The United States; Wake Up America! Your Liberties Are in Danger!” This side explained that the United States outlawed slavery and involuntary servitude. The other side was titled "Assert Your Rights" and it urged people to defend their rights. The two arguments were used to convince people of rejecting conscription as illegal.
This was particularly significant because of what was happening in the United States and Europe at this time. Europe was in the midst of World War I, and therefore, needed as much help and soldiers as it could get. On the other hand, the United States had recently entered World War I as well, and wanted to send more soldiers to Europe to support the war effort. This led to the passage of the Espionage Act, which made it illegal to make or convey false reports during wartime, particularly if these were intended to interfere with war operations or the success of the United States.