Constitution of the Republic of China (Taiwan) Article 4

The territory of the Republic of China according to its existing national boundaries shall not be altered except by resolution of the National Assembly.
中文原文 中華民國憲法第4條
中華民國領土依其固有之疆域,非經國民大會之決議,不得變更之。

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