Underground is a 1976 documentary film about the Weathermen, founded as a militant faction of the Students for a Democratic Society (SDS), who fought to overthrow the U.S. government during the 1960s and 1970s. The film consists of interviews with members of the group after they went underground and footage of the anti-war and civil rights protests of the time. It was directed by Emile de Antonio, Haskell Wexler and Mary Lampson, later subpoenaed by the Federal Bureau of Investigation in an attempt to confiscate the film footage in order to gain information that would help them arrest the Weathermen. (Wikipedia)

"The Film The FBI Didn't Want You To See"