Marie Martha Schlag (née Press; 26 February 1875 – 14 June 1956) was a German politician (SPD, KPD, SED). During the Weimar period she sat as a member of the Saxony regional parliament (Sächsischer Landtag). Later, in April 1946, she was a delegate at the party conference which enacted the contentious merger that gave rise to the Socialist Unity Party (SED), after 1949 the ruling party in a new kind of one-party dictatorship, the Soviet sponsored German Democratic Republic.