This paper investigates the effects of firm-level gender equality bargaining on the motherhood penalty using French administrative data. To tackle the endogeneity issue, we exploit the 2010 reform that introduced financial penalties for firms with 50 employees or more not complying with their obligation of negotiating on gender equality. This change led to a strong acceleration of gender equality bargaining after 2010 but only for firms with 50 employees or more. As a consequence, women who had their first child in concerned firms after 2010 are more likely to be employed in firms covered by a text related to gender equality. Controlling for firms' size effect and time trends as well as a set of other individuals' and firms' characteristics, we identify the causal effect of gender equality bargaining on earnings impact of motherhood. Our estimates show that forcing firms to promote measures related to gender equality has reinforced the motherhood penalty. While the causal effect of this reform is close to zero just after the first child birth, it turns out to be significantly negative 5 years after. Our results suggest that some measures mentioned in GE texts, especially those favouring work-life balance, may act as an indirect discrimination towards mothers.