N.Y.C. Charter § 818: 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.