Act Governing Relations with Hong Kong and Macau Article 26

Civil aircraft registered in the Republic of China, Hong Kong or Macau may fly between the Taiwan Area and Hong Kong or Macau with permission from the Ministry of Transportation and Communications. However, in the event of changes in circumstances which possibly threaten the security of the Taiwan Area or constitute a major concern, the Ministry of Transportation and Communications may impose necessary restrictions or prohibitions.Civil aircraft registered in Hong Kong or Macau which illegally enter the restricted areas of the Taipei Flight Information Region shall be warned or forced to leave the area, forced to land, or subjected to other necessary measures taken by agencies in charge of air defense.
中文原文 香港澳門關係條例第26條
在中華民國、香港或澳門登記之民用航空器,經交通部許可,得於臺灣地區與香港或澳門間飛航。
但基於情勢變更,有危及臺灣地區安全之虞或其他重大原因,交通部得予以必要之限制或禁止。
在香港或澳門登記之民用航空器違反法令規定進入臺北飛航情報區限制進入之區域,執行空防任務機關得警告驅離、強制降落或採取其他必要措施。

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