Although the tax system is not marriage neutral in many countries, it has been found only slightly significant in determining marriage decision (Buffeteau and Echevin, 2003; Alm and Whittington, 1995). This paper tests if the tax system could alter the decision to contract a civil union, which is a less binding marital contract. In France, since 1999, couples can either contract a marriage or a civil union (pacs). I assess the impact of taxation on the decision to contract a pacs using a difference-in-differences evaluation of the 2005 reform of income taxation of newly pacsed couples. As the control group is contaminated by the reform, I propose an original estimation method based on a difference-in-differences-in-differences setting to estimate bounds to the impact of the reform. My results suggest a positive and increasing impact of taxation on pacs rates, but also a change in the timing of pacs indicating that taxation alters the decision to contract a pacs. I find a slightly significant impact of taxation on the decision to break up a pacs
