25 Pa. Stat. § 2950
Whenever, pursuant to the provisions of The General County Law, the Governor certifies a change of classification to any county, the board of county commissioners shall, immediately after the recording of such change, notify the county board of elections of the change in classification. The board of elections shall thereupon promptly ascertain all county offices to be filled at the ensuing municipal election as a result of the impending change in classification and any existing county offices which are not to be filled at said election. For this purpose, it shall be the duty of the chairman of the county committee of each party to send to the board a written notice setting forth all party offices to be filled in the county at the ensuing municipal election.
25 P.S. § 2950