The workers are calling for a wage of $15 an hour and the right to form a union. Organizers of the walkout say cashiers, cooks and crew members at fast-food restaurants are paid a median wage of $8.94 an hour.

Since some 200 workers walked off their jobs at fast-food restaurants in New York City in November, the strikes have moved across the country, drawing attention to a fast-growing segment of the workforce that until recently had shown no inclination to organize for purposes of collective bargaining.

The planned August walkout — timed for the immediate aftermath of the 50th anniversary of the March on Washington for Jobs and Freedom and the lead-up to Labor Day — is expected to touch 35 or more cities and involve thousands of workers, organizers said. The walkouts have not led to widespread changes, though some workers say they have gotten small pay increases and better hours in the wake of previous strikes.