53 Pa. Stat. § 23449
Vacancies in positions in the competitive class shall be filled, so far as practicable, by promotions from among persons holding positions in a lower grade in the department, office, or institution in which the vacancy exists. Promotions shall be based upon merit, to be ascertained by tests to be provided by the civil service commission, and upon the superior qualifications of the person promoted, as shown by his previous service and experience. The commission shall have the power to determine, in each instance, whether an increase in salary constitutes a promotion. No promotion shall be made to a position in the competitive class, from a position in another class, except after such competitive examination and certification as is provided for original entrance to the competitive class: Provided, however, That persons holding positions in the labor class may be promoted to positions in the lowest grade of the competitive class upon promotion examinations as provided in this section, when such examination is specifically authorized by the commission. No person shall be promoted to a position for original entrance to which there is required, by this act or the rules adopted pursuant thereto, an examination involving essential tests or qualifications different from or higher than those required for original entrance to positions held by such persons, except as above provided.
53 P.S. § 23449