Whenever the population of any city of the second class A has regressed to a figure below the minimum fixed for that classification, the court of common pleas of the county in which the city is located shall, upon petition of fifteen per cent of the registered voters of the city or upon petition of the city council, appoint a charter commission to study and make recommendations on the adoption of a form of city government. Any city operating under a home rule charter or optional plan of government pursuant to the act of April 13, 1972 (P.L. 184, No. 62),¹ known as the “Home Rule Charter and Optional Plans Law,” shall retain its form of government as adopted until amended or repealed in accordance with the terms of the “Home Rule Charter and Optional Plans Law,” regardless of any change in classification under this act.