Part-time workers and workers hired for short periods of time are treated the same as full-time employees, for federal income tax withholding and social security, Medicare, and FUTA tax purposes.

Generally, it doesn't matter whether the part-time worker or worker hired for a short period of time has another job or has the maximum amount of social security tax withheld by another employer. Income tax withholding may be figured the same way as for full-time workers.