Federal tax deductions

@Don F  Well, for a start, they could try doing Single with 0 dependents, or putting an amount in for Extra Withholdings on their W-4. Maybe mark the box for 2 Jobs.

Unless you're paying them $30.00/hr or higher, there is basically no chance that a part-time employee claiming Married/3 is going to make enough gross pay on a paycheck to have Federal Withholding.

It's designed to not hold out federal income tax unless it expects you to owe federal income tax, and a $28,000+ standard deduction plus a $6,000 tax credit is a bit much for most part-timers to overcome.

Either way, their first step is going to be filling out a new W-4.