Senate Minority Leader Alan Peter Cayetano warned that the impeachment trial of Vice President Sara Duterte could be placed in uncertainty if the Supreme Court does not immediately clarify the definition of a Senate “majority” in relation to impeachment proceedings.

Cayetano issued the warning following a manifestation filed before the Supreme Court on June 30, which seeks to affirm an earlier petition questioning the validity of the June 3 Senate session described by petitioners as a “rump session.”

The disputed session reportedly involved the presence of Senator Francis “Chiz” Escudero and the formation of a bloc of 12 senators, which led to Cayetano’s removal as Senate President and the subsequent election of Senator Sherwin "Win" Gatchalian as Senate President Pro Tempore, before the latter assumed the Senate presidency during a June 17 special session.

Under the Constitution, a conviction in an impeachment trial requires a two-thirds vote of all Senate members, or at least 16 votes. However, concerns were raised that the required threshold could be affected if the number of active senators is reduced or redefined following recent political developments.

With the Senate currently composed of 22 members, proposals have reportedly emerged suggesting a lower conviction threshold, depending on membership changes within the chamber.

The developments come amid heightened political tension in the Senate, including the detention of Senator Jinggoy Estrada and possible legal actions involving Senator Rodante Marcoleta.