On May 28, 1898, the Philippine flag was first unfurled after the Philippine Revolutionary Army defeated Spanish forces in the Battle at Alapan, Imus, Cavite. The national flag was yet to be formally announced on the day of that battle. It was formally presented to the people on June 12, 1898. From 1919, when the Philippine flag was once more legalized, until 1940, Flag Day was observed in October, the date the Philippine Legislature had restored the flag. From 1941 to 1964, Flag Day was commemorated on the date the national flag was unfurled in Kawit: June 12.
However, in 1965, since Flag Day coincided with Independence Day, in order to commemorate the date the national emblem was first unfurled in battle, President Diosdado Macapagal issued Proclamation No. 374, 1965, which moved National Flag Day to May 28.
On May 23, 1994, President Fidel V. Ramos issued Executive Order No. 179, stretching National Flag Day into an extended period, from May 28 to June 12, culminating in the celebration of Independence Day. 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.
Executive Order No. 179, 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: The Flag and Heraldic Code of the Philippines