Political Parties Act Article 15

A party congress composed of party members shall act as the highest authority of a political party. Political parties shall convene a party congress not less than once every two years.Representatives to a party congress shall be selected by the members of the political party pursuant to the party charter. The authority of the party congress shall be exercised by convening the party representatives.
中文原文 政黨法第15條
政黨以黨員大會為最高權力機關。
黨員大會至少每二年召開一次。
前項黨員大會,得依章程規定由黨員選出代表,召開黨員代表大會,行使黨員大會職權。

English translation for reference only; the Chinese text prevails. Not legal advice.