They were convicted in 1954 of violating the Smith Acting, which outlawed “teaching or advocating the overthrow of the American government by force.” He served over a year at the federal penitentiary at Allenwood, Pennsylvania, before the Justice Department withdrew charges in 1958. After 1958, Klonsky lived in California, where he ran a bookstore near University of California, Los Angeles and where he remained active in organizing workers in the film industry. Robert Klonsky supported jailed professor Angela Davis, demonstrated against the Vietnam War, and had a few acting parts in movies.
He and other survivors of the Spanish war were made honorary citizens of Spain in 1998.
Klonsky died September 7, 2002 in Chicago at the age of 84.