People’s Initiative or "PI" is one of the modes provided in the 1987 Constitution of the Philippines for constitutional amendment. The other two modes are via Constituent Assembly or "Con-Ass" and Constitutional Convention or "Con-Con", which also allow revisions.
Under Article XVII, Sec.2 of the Constitution,
“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 votes 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.”
The process of amending the 1987 constitution of the Philippines is popularly known to many Filipinos as Charter Change. Any proposed amendment or revision to the 1987 Constitution shall only be valid when ratified by the majority of Filipinos in a plebiscite.
HOWEVER, congress has not passed a law providing for the implementation of the exercise of this right and hence can not be evoked as issues arise. Issues such as who verifies that the petition is by at least twelve per centum of the total number of registered votes or which government office processes the petition hinder the exercise of this provision.
- The 1987 Constitution Of The Republic Of The Philippines 
- Article XVII, the 1987 Constitution of the Philippines 
- Abs-Cbn Interactive, New people's initiative drive eyes revision, not amendment
- The Philippines' Initiative and Referendum Act (Republic Act 6735)