24 Pa. Stat. § 588.7
If for any reason the tax imposed by this act or any other tax imposed on a person's earnings by school districts of the first class A is not paid when due, interest at the rate of six per centum per annum on the amount of said taxes or interest at a per annum rate which does not exceed the Federal Reserve Discount Rate in effect for Federal Reserve District Four on December 1 of the preceding tax year, whichever is greater, and a penalty of one-half of one per centum of the amount of the unpaid taxes for each month or fraction thereof during which the taxes remain unpaid, shall be added and collected. If, however, a person or an employer does not make required deductions and remittance of tax money under section 4 of this act, that person shall be subject to, in lieu of the penalty amount under this section and in addition to the interest amount under this section, an additional penalty of five per centum of the amount of the unpaid taxes for each month or fraction thereof during which the taxes remain unpaid, and this amount shall be added and collected: Provided, That the additional penalty imposed herein shall not exceed fifty per centum of the unpaid taxes. A school district shall, on or before December 31, establish by resolution the specific per annum interest rate to be imposed on unpaid taxes during the following tax year. Where suit is brought for the recovery of any such tax, the person liable therefor shall, in addition, be liable for the costs of collection and the interest and penalties herein imposed.
24 P.S. § 588.7