The Federal Bureau of Investigation (FBI) opened a file on Oppenheimer in March 1941. It recorded that he attended a meeting in December 1940 at Chevalier's home that was also attended by the Communist Party's California state secretary, William Schneiderman, and its treasurer, Isaac Folkoff. The FBI noted that Oppenheimer was on the executive committee of the American Civil Liberties Union, which it considered a communist front organization. Shortly thereafter, the FBI added Oppenheimer to its Custodial Detention Index, for arrest in case of national emergency.