Enforcement Rules for the Act Governing Relations between Peoples of the Taiwan Area and the Mainland Area Article 28

The suspension of entitlement to retirement benefits (from employer or the military) as referred to in Paragraph 3 of Article 26 of the Act shall mean that the said entitlement is suspended from the time when a retiree from the military, government, state enterprise or educational institution obtains household registration in the Mainland Area or holds a passport issued by the Mainland Area; any overpaid amount shall be reclaimed.
中文原文 臺灣地區與大陸地區人民關係條例施行細則第28條
本條例第二十六條第三項所稱停止領受退休(職、伍)給與之權利,指支領各種月退休(職、伍)給與之退休(職、伍)軍公教及公營事業機關(構)人員,自其在大陸地區設有戶籍或領用大陸護照時起,停止領受退休(職、伍)給與;如有溢領金額,應予追回。

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