The payroll obligations of each school district shall be preferential claims. It shall be the duty of the board of school directors of each district to provide for the payment of payroll obligations before authorizing the payment of any other current expense except for fuel, water, electric service, or such supplies as are actually essential for keeping the schools in session. In order to meet payroll requirements the board shall, if necessary, negotiate such short term loans as are necessary and possible in accordance with the law governing the borrowing powers of the district.

In the event the payment of salaries of employes of any school district is not made when due, the school district shall be liable for the payment of same, together with interest at six percentum (6%) per annum from the due date: Provided, That no school district shall be required to pay interest on unpaid salaries, if the failure to pay salaries is occasioned by the failure of the Commonwealth to make payment of semi-annual allotment of appropriation at the time that such payment is due.