They say the policy applies to all "interns, volunteers, substitutes, and contractors."
Officials say the decision was made in accordance with Centers for Disease guidelines, as well as those of state and local health officials.
Unvaccinated employees must be tested weekly. Tests will be conducted at no cost to the employee.
Numerous state and county governments – as well as businesses in the private sector – are mandating vaccinations for employees in the wake of the arrival of the super-contagious Delta variant.