Postal Act Article 19

Unless acting in accordance with the law, Chunghwa Post Co., Ltd may not refuse to accept and deliver mail items provided in the subparagraphs of paragraph 2 of Article 5-1, except for material or mail items which do not meet the specifications publicly announced by Chunghwa Post.
中文原文 郵政法第19條
中華郵政公司非依法規,不得拒絕遞送第五條之一第二項各款之文件或物品。
但禁寄物品或郵件規格不符中華郵政公司公告者,不在此限。

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