Because the producers feared both sabotage and destruction of the film, the exposed footage had to be developed in secret, at night, by a sympathetic lab technician, with the film delivered in unmarked canisters.
Because blacklisted people were among those who made the movie, the production was fraught with interference by local thugs. The entire cast and crew were met by a citizens' committee in Central (now Santa Clara), New Mexico, where they had planned to film, and were ordered to leave town. The following day they moved the production to Silver City, NM, and were warned to "get out of town... or go out in black boxes."
This movie was the only blacklisted film ever in American film history. It was blacklisted in the 1950s at the height of the McCarthyism scourge.
Director Herbert J. Biberman, screenwriter Michael Wilson, producer Paul Jarrico, and composer Sol Kaplan made the film largely in retaliation for being blacklisted. Since they weren't allowed to work in Hollywood, they reasoned they'd might as well make a film as pro-Communist as possible, to fit the "crime" for which they had been accused by the Un-American House Activities Committee.
Rosaura Revueltas was a noted screen actress in her native Mexico. After this film was distributed, she was accused of being a Communist and deported. She continued to appear in Mexican cinema, but never made another film in the US.