In German-occupied areas, the Nazis singled out Jewish laborers for cruel treatment. Jewish laborers were also subjected to humiliating treatment, as when SS men forced religious Jews to submit to having their beards cut. The ghettos served as bases for utilizing Jewish labor, as did forced-labor camps for Jews in occupied Poland. In the Lodz ghetto, for example, the Nazis opened 96 factories. The ability to work could save one's life, but most often only temporarily. Jews deemed unproductive by the Nazis were often the first to be shot or deported. Jewish labor, even forced labor, was considered expendable. The extermination of the Jews became the singular priority of the Nazis.
The Nazis exploited the forced labor of "enemies of the state" for economic gain. Labor shortages in the German war economy became critical especially after German defeat in the battle of Stalingrad in 1942-1943. This led to the increased use of prisoners as forced laborers in German industries. Especially in 1943 and 1944, hundreds of camps were established in or near industrial plants.
Camps such as Auschwitz in Poland and Buchenwald in central Germany became administrative centers of huge networks of forced-labor camps. In addition to SS-owned enterprises (the German Armament Works, for example), private German firms -- such as Messerschmidt, Junkers, Siemens, and I. G. Farben -- increasingly relied on forced laborers to boost war production. One of the most infamous of these camps was Auschwitz III, or Monowitz, which supplied forced laborers to a synthetic rubber plant owned by I. G. Farben. Prisoners in all the concentration camps were literally worked to death.
Sources: U.S. Holocaust Memorial Museum