53 Pa. Stat. § 23440
The civil service commission, is each city of the second class, shall make rules and regulations providing for examinations for positions in the classified service of each city, and for appointments to and promotions therein, and for such other matters as are necessary to carry out the purposes of this act. Due notice of the contents of such rules and regulations and of any modifications thereof shall be given, by mail, in due season, to appointing officers and heads of departments affected thereby; and said rules and regulations and modifications thereof shall also be printed for public distribution. All original appointments to the competitive and noncompetitive classes of the service shall be for a probationary period of three months: Provided, however, That at any time during the probationary period the appointee may be dismissed for just cause, in the manner provided in section twenty. If at the close of this probationary term, the conduct or capacity of the probationer has not been satisfactory to the appointing officer, the probationer shall be notified, in writing, that he will not receive absolute appointment, whereupon his employment shall cease; otherwise, his retention in the service shall be equivalent to his final appointment.
53 P.S. § 23440