> With its depiction of unfair banking and labor practices, Steinbeck's novel was already controversial before 20th Century-Fox brought it to the screen. It was banned in several states and counties, and the library in Steinbeck's hometown -- Salinas, CA -- refused to carry it until the 1990s. When Fox announced the film version, The Associated Farmers of California and the Agriculture Council of California threatened to boycott the studio's films, and Steinbeck received death threats. To tone down political message, Zanuck and screenwriter Johnson focused the film on the Joad family and its struggle to survive.

> At the time, all scripts and films produced for distribution to major theaters in the U.S. had to be passed by the Production Code Administration (PCA). Created by the major studios, the PCA safeguarded films from local censorship by keeping out offensive and controversial materials before they were released. The studios could not release a film without the PCA's Seal of Approval, and to get it they often had to rewrite scripts and reedit completed films. For The Grapes of Wrath, Johnson had to tone down some of the novel's earthier passages. For example, when Tom discovers his sister Rosasharn is pregnant, Steinbeck had him say, "Well, I see you been busy." That was too suggestive for the Production Code, so it was changed to "Well, I see I'm gonna be an uncle soon." One character's take on the popular song "Yes, Sir, That's My Baby" as "Yes, Sir, That's My Savior" had its lyrics replaced by humming with the occasional singing of "my Savior," for fear audiences would think it mocked Christianity. Code officials also suggested the studio cut the novel's references to Tulare County and the city of Pixley, too areas in California notorious for their mistreatment of migrant workers.

> The plot also underwent a little brightening to make the film less downbeat than the novel, which had ended with the Joad family split apart by hard times. By reordering some scenes, Johnson left the impression that they would prosper once they found a good, government-run work camp. There was no way a Hollywood studio in 1940 could have filmed the novel's conclusion, in which Rosasharn loses her baby and then breastfeeds a starving man. In addition, Zanuck wanted something more uplifting. In its place, he told Johnson to take a speech Ma Joad makes about the strength of "the people" from its position about two thirds of the way through the novel and use that at the picture's end. Ford was appalled at the idea and said it would only get in the film if Zanuck directed it himself, so he did. Years later, Ford would state that Tom Joad's final scene was the real end of the film for him, but that the final scene was "all right."