If an employee has agreed to work a shift in addition to their normal rostered shifts but gets sick, does the employee have to take paid sick leave, or can they choose to not be paid?
If the employer and the employee have agreed that the employee will work these hours, then the employee is entitled to paid sick leave.
If the employee wants to take unpaid leave instead of using their paid sick leave entitlement, you can agree to this. It would be best to keep a written record of this agreement.