As the grape strike neared a boiling point in late 1967, Chavez became increasingly concerned about the union's ability to keep UFW strikers under control. After two and a half years of protest, the union had only nine winery contracts to show for its efforts, and morale was unraveling. Chavez' greatest fear was that the discipline of non-violence that he had insisted upon from the beginning was falling apart. Scattered incidents of violence by picketers against scabs and and growers only increased his fears, and he decide he must take radical action to maintain non-violence. He decided to begin a fast that would not end until all UFW members had renewed their commitment to this discipline. Chavez had long been a disciple of Gandhi, and this action had great appeal to him.

He began his fast quietly on February 15, 1968, breaking the news to his followers at a tumultuous meeting four days later. The fast would later be viewed as a defining moment for the union, one that renewed its sense of hope and unity and restored the power of nonviolence. At the time, however, some of the union's other leaders refused to talk to Cesar because they thought the fast was an absurd waste of time. But within a few days union leaders rallied to Chavez's side fanning out across the valley to tell members about the purpose of the fast and to invite them to the Forty Acres compound to show their support. The response was overwhelming. Thousand of farm workers streamed to the Forty Acres with crucifixes and other offerings, pledging support and imploring Chavez to stay alive and healthy. People slept in tents pitched in the yard and at night had festive prayer rallies with singing and hot chocolate. According to Leroy Chatfield, "The irony of the fast was that it turned out to be the greatest organizing tool in the history of the labor movement ...workers came from every sector of California and Arizona to meet with Cesar, to talk to him about the problems of their areas...Cesar had more organizing going on while he was immobilized ..than had ever happened before in the union."

On day thirteen of the fast, Cesar was forced out of bed by a Kern County Superior Court order to answer contempt charges. But the show of support left authorizes befuddled: More than three thousand farmworkers packed the corridors of the courthouse and knelt in quiet prayer outside. Contempt charges were dropped by Guimarra Wineries.

On March 11, Chavez ended his fast at a rally of six thousand supporters at a park in Delano. Robert Kennedy flew in to celebrate the occasion, and sat next to Cesar who was wrapped in a blanket. The two men, both Catholics, shared a piece of bread blessed by a priest. (This account is taken from "The Fight in the Fields," by Susan Ferriss and Richard Sandoval.)