The Nazi-Soviet Non-Aggression Pact of August 23, 1939, deeply shook Lash's growing leanings towards the Communist Party, causing him to resign as executive secretary of the American Student Union. Three months later he was subpoenaed to appear before the House Un-American Activities Committee (colloquially known as the "Dies Committee" after its chairman) to be questioned about his activities with the American Student Union and the American Youth Congress. Lash was a hostile witness on November 11, refusing to cooperate with the committee in its effort to obtain the names of members of the Communist Party and to expound upon their influence.