 Hammann was elected to the town council in 1928 and to the landtag of Hesse in 1927.In 1930 he was banned from teaching and imprisoned for one month after opposing police suppression of a strike at Opel plant in Rüsselsheim.In 1932 he was convicted for a second time, but the sentence was suspended, perhaps as a precaution against the buildup of Nazi influence.