The sheriff of any county with a population of less than twelve thousand five hundred which has not adopted civil service for deputy sheriffs pursuant to the provisions of section nineteen, article fourteen, chapter seven, may allow his deputy sheriffs to do additional police work in addition to their normal duties as a deputy sheriff. However, they may not be allowed to engage in such police work for any party engaged in or involved in any labor trouble or dispute between employer and employee. Before such sheriff shall be allowed to grant such additional police work to his deputy sheriffs, he must prepare a plan setting forth the terms and conditions under which his deputy sheriffs may engage in additional police work. Such terms and conditions must prohibit discrimination between deputies with regard to the allocation of additional police work. Such plans shall be submitted to the county commission of such county and shall be subject to the approval of said county commission. No sheriff may have a direct or indirect pecuniary interest in any outside employment. A deputy sheriff performing additional police work shall wear an identifying armband to indicate special duty.