In each county of the first class, the salaries of the guards, keepers, industrial officers and guard orderlies, employed in the jails, houses of detention and penitentiaries, shall be not less than $2,000.00 per annum and shall not exceed $6,000.00 per annum, with provision for increments in salary between the minimum and maximum of such salaries to be fixed by the board of chosen freeholders.
This section shall not be construed to permit the decrease of any salaries now authorized by law to be paid to any of the guards, keepers, industrial officers and guard orderlies, affected by this section nor decrease the amount of each increment now being paid.