For students who face marginalization in a discipline, counterspaces are safe spaces of refuge that allow them to express their multiple identities and foster their sense of belonging. While prior qualitative work on counterspaces has highlighted how and why these spaces support marginalized students, there is little quantitative work that provides systemic evidence on broad counterspace initiatives formed to support students' disciplinary sense of belonging. In physics, a discipline that is deeply androcentric, two potential counterspaces have emerged for undergraduate women: the Conferences for Undergraduate Women in Physics (CUWiP) and Women in Physics Groups (WiPG). Drawing on survey data collected from undergraduate women in physics programs across the country who were registering for the 2018 CUWiP (N = 1388), we used structural equation modeling to test the effect of earlier participation in CUWiP and WiPG on students' current sense of belonging and interest in physics. We also tested the mediating effect of believing that there are serious gender issues in physics since these spaces have been found to increase students' consciousness of gender bias. The results revealed a significant positive direct effect of CUWiP and WiPG on sense of belonging. A more complex story emerged for indirect effects where believing in serious gender issues can negatively affect sense of belonging if interest in physics is not positively reinforced. Overall, the findings clearly provide quantitative evidence that broad diversity conference and affinity group initiatives, such as CUWiP and WiPG, can act as counterspaces that bolster belonging for women in disciplines like physics where they are marginalized. However, activities in these spaces should also continue to foster students' unique disciplinary interests.