Sick pay and sick leave are taxable compensation when representing your regular wages.  Your employer must include them as compensation and withhold Pennsylvania tax. 

Payments, not representing regular wages, including payments made by third party insurers for sickness or disability, are not taxable income for Pennsylvania purposes.  Your employer should not include periodic payments for sickness or disability in Box 16 of your W-2 Form.  If your employer includes this income and withholds Pennsylvania tax, you must obtain and submit a corrected W-2 Form or a statement from your employer explaining the error.