By the 1950s, the GDR began to tighten its emigration laws and stigmatize Republikflucht in an attempt to curtail legal emigration, including requiring de-registration with East German authorities and permission to the leave the country under threat of prison sentences up to three years. A propaganda booklet published by the GDR's ruling Socialist Unity Party of Germany (SED) in 1955 for the use of party agitators outlined the seriousness of "flight from the republic":