The activists began the "Fast for Safe Schools" on Monday. They intend to drink only water until the city and state provide enough money to rehire about 1,200 lunchtime aides.
The workers are among more than 3,800 district employees who will be laid off June 30 because of a $304 million deficit.
Hunger strikers plan to camp outside Gov. Tom Corbett's office in Philadelphia during the daytime and sleep at a nearby church at night.
The fast is being organized by Unite Here, a union that represents the aides and 700 food service workers.
Mayor Michael Nutter has been lobbying City Council and state lawmakers for additional funds.
