On March 6, 1965, Presidential Proclamation No. 374 was issued declaring May 28 as National Flag Day to commemorate the date the national emblem was first unfurled after the Philippine Revolutionary Army defeated the Spanish fores in the Battle at Alapan, Imus, Cavite in 1898. On May 23, 1994, Executive Order No. 79 was issued extending the period of celebrating National Flag Day from May 28 to June 12. All Filipinos are encouraged to display the Philippine flag in all offices, agencies and instruments of government, business establishments, schools, and private homes throughout this period.
The Presidential Spokesperson’s 2011 statement on the Flag Days:
Display our national colors on the Philippine Flag Days, May 28 to June 12.
Executive Order No. 79, s. 1994:
Ordering the prominent display of the national flag in all buildings, establishments, and homes from 28 May 1994 to 12 June 1994 and every year thereafter, and for other purposes.
Executive Order No. 310:
Prescribing the design and use of the Coat-of-Arms, Seal, and Flag of the President and Vice President of the Philippines, and for other purposes.
Republic Act No. 8491:
Flag and Heraldic Code of the Philippines.