Section 818. Power of investigation

The commissioner shall have the power
  to make investigations concerning all matters touching  the  enforcement
  and  effect  of  the  provisions  of the civil service law insofar as it
  applies to the city and the rules and regulations prescribed thereunder,
  or concerning  the  actions  of  any  examiner  or  subordinate  of  the
  department,  or  of any officer or employee of the city or of any county
  within the city, in respect to the execution of the civil  service  law;
  and in the course of such investigations the commissioner shall have the
  power to administer oaths, to compel the attendance of witnesses, and to
  examine such persons as deemed necessary.