Collective Agreement Act Article 22

During the effective period of labor contract if the interested parties of a collective agreement abandon their rights obtained from a labor contract that are resulting from the collective agreement, their abandonment shall be null and void. Provided that, if the rights are not exercised within three months after the termination of labor contract, those rights can no longer be exercised.When an employer is bound by a collective agreement, it he/she terminates a labor contract because a worker claims the rights that are arising from the collective agreement or the rights that are contained in a labor contract resulting from a collective agreement, the termination shall be null and void.
中文原文 團體協約法第22條
團體協約關係人,如於其勞動契約存續期間拋棄其由團體協約所得勞動契約上之權利,其拋棄無效。
但於勞動契約終止後三個月內仍不行使其權利者,不得再行使。
受團體協約拘束之雇主,因勞工主張其於團體協約所享有之權利或勞動契約中基於團體協約所生之權利,而終止勞動契約者,其終止為無效。

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