People’s Initiative or "PI" is one of the modes in which the 1987 Constitution of the Philippines

Constitution of the Philippines

The Constitution of the Philippines is the supreme law of the Philippines.The Constitution currently in effect was enacted in 1987, during the administration of President Corazon Aquino, and is popularly known as the "1987 Constitution"...

 could be amended. The other two modes are via Constituent Assembly

Constituent Assembly (Philippines)

Constituent assembly or "con-ass" is one of the three modes in which the 1987 Constitution of the Philippines could be amended or revised. The other two modes are via People's Initiative and Constitutional Convention...

 or "Con-Ass" and Constitutional Convention

Constitutional Convention (Philippines)

Constitutional convention or “con-con” is one of the three modes in which the "Constitution of the Philippines could be amended or revised. The other two modes are via a People's Initiative or "PI" and Constituent Assembly or "Con-Ass"....

 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.”

The process of amending or revising 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.