Article 239 of the Taiwan Criminal Code stipulates, "Anyone who has a spouse and commits adultery with another person shall be punished by imprisonment for a term not exceeding one year. The same applies to those who commit adultery." This Interpretation overrules J.Y. Interpretation No. 554 (2002), which affirmed the constitutionality of the Criminal Code’s restriction on individual sexual freedom on the grounds that such freedom was subject to restriction for the purpose of protecting the marriage and family. In this Interpretation, the Court expanded the scope of sexual autonomy under Article 22 of the Constitution and held that the infringement of the rights to sexual autonomy and of individual privacy by the criminalization of adultery fail the proportionality test in the Constitution’s Article 23. The Court found Article 239 unconstitutional because it restricted an individual's freedom to decide whether and with whom to engage in sexual activity. However, the state should generally limit the punishments for illegal acts to those detrimental to social order or public welfare. Therefore, while adultery is undoubtedly detrimental to the obligation of fidelity in a marriage and the feelings and expectations of the other party, it is not clearly detrimental to the social order or public welfare. Further, adultery mainly occurs in private. The process of discovery, prosecution, and trial inevitably interferes with personal privacy, driving the state's public power straight into the very private space of the people. Therefore, the Court found that the regulation causes more significant damage than the interest it intends to protect. This case is important not only in its recognition of a constitutionally-protected right to sexual autonomy and its emphasis on individual privacy but also because the Criminal Code provisions on adultery reportedly had been applied disproportionately against women and also to pressure women not to pursue sexual assault charges, which could lead to the woman becoming charged with adultery.
刑法第239條規定:「有配偶而與人通姦者,處1年以下有期徒刑。其相姦者亦同。」本解釋推翻司法院第554號解釋(2002),關於保障婚姻和家庭而限制個人性自主權利之合憲性解釋。憲法法庭認憲法第22條所保障性自主權之限制,與憲法第23條比例原則不符,應自本解釋公布之日起失其效力;於此範圍內,本院釋字第554號解釋應予變更。因而宣告此一規定違憲。此規定立法目的係限制個人得自由決定是否及與何人發生性行為之性行為自由。然基於刑法謙抑性原則,國家原則上應以侵害公益或大眾福祉之違法行為為限。因此,通姦行為固已損及婚姻關係中之忠誠義務及對方之感情與對婚姻之期待,但尚不致明顯損及公益或大眾福祉。再者,通姦行為多發生於個人之私密空間內,其發現、追訴、審判過程必然侵擾個人生活私密領域,致國家公權力長驅直入人民極私密之領域。因此,系爭規定所致之損害大於其目的所欲維護之利益,而有失均衡。本案宣告違憲之重要性不僅在於對於憲法上所保障的性自主權及隱私權的再次確認,更是因為刑法通姦罪適用上對於女性比例上多於男性被告,及適用上經常迫使女性放棄追溯之實證結果,而不符合憲法所保障之意旨。