Only Filipino citizens or corporations or associations at least seventy per centum of the capital of which is owned by such citizens shall be allowed to engage in the advertising industry. The participation of foreign investors in the governing body of entities in such industry shall be limited to their proportionate share in the capital thereof, and all the executive and managing officers of such entities must be citizens of the Philippines. Section 12. The Congress may create a consultative body to advise the President on policies affecting indigenous cultural communities, the majority of the members of which shall come from such communities. ARTICLE XVII AMENDMENTS OR REVISIONS Section 1. Any amendment to, or revision of, this Constitution may be proposed by: (1) The Congress, upon a vote of three-fourths of all its Members; or (2) A constitutional convention. Section 2. Amendments to this Constitution may likewise be directly proposed by the people through initiative upon a petition of at least twelve per centum of the total number of registered voters, of which every legislative district must be represented by at least three per centum of the registered voters therein. No amendment under this section shall be authorized within five years following the ratification of this Constitution nor oftener than once every five years thereafter. The Congress shall provide for the implementation of the exercise of this right. Section 3. The Congress may, by a vote of two-thirds of all its Members, call a constitutional convention, or by a majority vote of all its Members, submit to the electorate the question of calling such a convention. Section 4. Any amendment to, or revision of, this Constitution under Section 1 hereof shall be valid when ratified by a majority of the votes cast in a plebiscite which shall be held not earlier than sixty days nor later than ninety days after the approval of such amendment or revision. Any amendment under Section 2 hereof shall be valid when ratified by a majority of the votes cast in a plebiscite which shall be held not earlier than sixty days nor later than ninety days after the certification by the Commission on Elections of the sufficiency of the petition. ARTICLE XVIII TRANSITORY PROVISIONS