Following the criminalization of the Assimilation Society in 1915, the new target of Taiwanese political activism was Law 63. Law 63 legally defined Taiwan as colonial space. The law granted the Governor General of Taiwan the power to issue ordinances that had the force of law. It granted the Government General the power, in other words, to circumvent representative government. In the inner territory, such power was reserved for the emperor. But in the colonies, Law 63 and Law 30, its Korean equivalent, empowered the Governments General to rule by decree.

In 1920, Cai, who had moved to Tokyo in 1915 to enroll in Tokyo Higher Normal School, joined with other members of the New People’s Society (Shinminkai) and the newly formed Taiwan Youth Association (Taiwan seinenkai) to lobby the Diet for the law’s permanent repeal. Contrary to their demands, however, in 1921 the Diet made the law permanent (now as Law 3).

With this avenue for political reform closed, Cai and the Taiwan Youth Association turned toward achieving even bigger changes in the distribution of political power in the Japanese Empire. In 1923, Cai, who had returned to Taiwan in 1922, joined other Taiwanese activists to petition the Taihoku Police for permission to establish a new organization, the League for the Establishment of a Taiwan Parliament (Taiwan gikai). The colonial police denied the petition. Cai then traveled to Tokyo, where he applied to the Tokyo Police for permission to establish the organization in Tokyo. The Tokyo Police granted his request, and the League for the Establishment of a Taiwan Parliament was born.

The League submitted petitions to the Diet for the establishment of a Taiwan parliament every year between 1921 and 1934 (the first petitions were filed by members of the New People’s Society, but without the organization’s name). Usually signed by one thousand to two thousand individuals, the petitions represented the voice of the socioeconomic middle ground of Taiwanese society, with over sixty percent of the signatories having completed elementary or elementary-equivalent education but no higher school or college. The Diet denied each petition (Chen 1972, 483-88).