A plebiscite on June 18, 1940 to ratify the following amendments to the Constitution: tenure of the President and the Vice-President was four years with reelection for another term; establishment of a bicameral Congress of the Philippines, with the Senate as the upper house and the House of Representatives as the lower house, and the creation of an independent Commission on Elections composed of three members to supervise all elections and plebiscites.
References
Philippine constitutional plebiscites, 1940 Wikipedia(Text) CC BY-SA