Act of Military Service for Officers and Non-commissioned Officers of the Armed Forces Article 53

Officers or Non-commissioned Officers receiving the retirement pay or pension and the bereaved dependents receiving Survivor Annuity, who has been lived in Mainland China for a long time but did not have household registration set up there or is not the holder of the passport of Mainland China, the giving authority shall suspend giving the monthly pension, alimony or Survivor Annuity during their time of living in Mainland China until they have applied in person for retirement pay in accordance with the regulations or return to Taiwan for living; then payment will be made in accordance with relevant regulations.
中文原文 陸海空軍軍官士官服役條例第53條
支領退休俸或贍養金之軍官、士官或支領遺屬年金之遺族赴大陸地區長期居住,而未在大陸地區設有戶籍或領用大陸地區護照者,支給機關應於其居住大陸地區期間,暫停發給退休俸、贍養金或遺屬年金,俟其親自依規定申請改領退伍金或回臺居住時,再依相關規定補發。

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