All cases involving the constitutionality of a treaty, international or executive agreement, or law, which shall be heard by the Supreme Court en banc, and all other cases which under the Rules of Court are required to be heard en banc, including those involving the constitutionality, application, or operation of presidential decrees, proclamations, orders, instructions, ordinances, and other regulations, shall be decided with the concurrence of a majority of the Members who actually took part in the deliberations on the issues in the case and voted thereon.