53 Pa. Stat. § 12628
The exempt class shall include positions, except that of unskilled laborer, for the filling of which the commission shall have found competitive examinations to be impracticable. No position shall be deemed to be in the exempt class unless and until the civil service commission, after a public hearing of which suitable public notice has been given, has determined that it is unable to obtain by competitive examination persons possessing the usual and requisite qualifications for filling such office or position, and has classified such office or position in the exempt class. The reasons for every such exemption shall be stated separately and at length in the annual reports of the civil service commission. Not more than one appointment shall be made to, or under the title of, any such office or position unless a different number is specifically authorized by the civil service commission. Appointments in the exempt class may be made without examination. The exempt class shall include the chief assistant to the head of each of the departments of government (except the civil service commission), one secretary or clerk appointed by the mayor, and one secretary or clerk appointed by each head of each department of the city government.
53 P.S. § 12628