"As early as 1900's, OFW's were already hired in different parts of the country. According to DOLE (Department of Labor and Employment), Filipinos were recruited temporarily to Hawaii due to unemployment issues. Moreover, some Filipinos worked in USA after WWII after they became American citizens after serving the US military. However, it was legalized after the Martial Law when President Marcos issued the New Labor Code on 1974. This was done to address unemployment problems and also to strengthen the Philippines' ties to other countries.
All about OFW in Philippines are also discussed here: