The assignment of enrollees shall not result in the displacement of currently employed workers, including partial displacement such as reduction in hours of nonovertime work, wages, or other employment benefits. Supervising agencies that participate in the program may not terminate, lay-off, or reduce the working hours of any employee for the purpose of utilizing an enrollee with funds available. In circumstances where substantial efficiencies or a public purpose may result, supervising agencies may utilize enrollees to carry out essential agency work or contractual functions without displacing current employees.