Supervisory employee means an employee, regardless of job description, having authority in the interest of the employer to hire, transfer, suspend, lay off, recall, promote, discharge, assign, reward, or discipline other employees, or the responsibility to assign work to and direct them, or to adjust their grievances, or effectively recommend that action, if, in connection with the foregoing functions, the exercise of that authority is not of a merely routine or clerical nature, but requires the use of independent judgment.