Dunn was an active member of the American Civil Liberties Union from its creation, serving on that group's National Committee from 1923 and on its board of directors from 1933 to 1941.
Dunn was the author of a number of books and pamphlets on economic themes relating to the working class published by the Communist Party USA.
[3] Dunn returned to the United States in May 1923, being closely questioned upon his arrival by an agent of the Justice Department's Bureau of Investigation, forerunner of the FBI.
[3] Although he was only found by the investigating authorities to be carrying statistical information about the Russian textile industry, Dunn returned to America a committed believer in the Soviet social and economic experiment.
[3] He was also a contributor to the periodic almanac published by the Rand School of Social Science, the American Labor Year Book, throughout the decade of the 1920s.