Administrative Appeal Act Article 28

One who has same interest at stake as an administrative appellant might participate the administrative appeal after the permission was granted by the agency with jurisdiction of administrative appeal. The agency with jurisdiction of administrative appeal might notify she/he to participate the administrative appeal while necessary as well.While an administrative appeal decision to revoke or modify the original administrative action which substantially affected the right or interest of the third party, the agency with jurisdiction of administrative appeal shall notify her/him to intervent the administrative appeal procedure and pose her/his opinion.
中文原文 訴願法第28條
與訴願人利害關係相同之人,經受理訴願機關允許,得為訴願人之利益參加訴願。
受理訴願機關認有必要時,亦得通知其參加訴願。
訴願決定因撤銷或變更原處分,足以影響第三人權益者,受理訴願機關應於作成訴願決定之前,通知其參加訴願程序,表示意見。

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