Regulations Governing Temporary Detention of Passengers Article 3

When the Agency implements temporary detention, the Agency shall inform the person for the temporary detention (hereinafter referred to as “the detainee”) the reasons for the temporary detention and the related law(s) which have been violated. The Agency will not require informing the detainee for the reasons of the temporary detention if it is deemed to not be appropriate.
中文原文 內政部入出國及移民署實施暫時留置辦法第3條
入出國及移民署實施暫時留置時,除有不宜告知者外,應先告知被暫時留置人實施暫時留置之事由及法令依據。

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