In recent years, a growing number of researchers have documented the emergence of an alternative form of ecumenism, in which morally conservative actors form cross-denominational alliances to defend "Christian values". Along with issues of gender and sexuality, migration is increasingly becoming an issue that polarizes liberal democratic societies along value lines. Particularly in North America, the religious right has been instrumental in promoting political leaders and parties that enact anti-immigrant policies and uphold a nativist political agenda. At the same time, it is also in the migration field that we see a new counter-movement to the "ecumenism of hate" emerging, which bears the potential to bridge religious divisions over a politics of humanitarian assistance and solidarity with migrants. Bringing together the literature on faith-based humanitarianism and new forms of ecumenism, this paper seeks to examine the possibilities and limitations of this new form of interreligious cooperation. Empirically, the paper zooms in on the religious networks that actively support migrants along the US-Mexico borderlands. It focuses on how local religious communities navigate contentious political debates autonomously from their institutional hierarchies, forming ecumenical, grassroots networks to address challenges of migration and social justice. Drawing on interviews with religious actors and analysis of primary documents, including reports and statements by religious organizations, the study argues that, at least in part, the collaboration of faith-based organizations from different religious traditions to provide humanitarian assistance to migrants at the border has generated a form of "ecumenism from below" that cultivates a distinctive form of religious and political solidarity that challenges anti-immigration narratives and seeks to construct an alternative to the rise of white Christian nationalism in the region.