Political Research Quarterly, Ahead of Print. Prior research suggests social ties with undocumented immigrants among Latinxs may increase political engagement despite constraints undocumented social networks may introduce. We build on prior research and find across six surveys of Latinxs that social ties with undocumented immigrants are reliably associated with collective, identity expressive activities such as protesting, but not activities where immigration may not be immediately relevant, such as voting. Moreover, we assess a series of mechanisms to resolve the puzzle of heightened participation despite constraints. Consistent with prior research at the intersection of anti immigrant threat and Social Identity Theory, we find Latinxs with strong ethnic identification are more likely to engage in political protest in the presence of social ties with undocumented immigrants, whereas weak identifiers disengage. We rule out alternative mechanisms that could link undocumented social ties with participation including political efficacy, a sense of injustice, linked fate, acculturation, outgroup perceptions of immigration status, partisan identity, conducive opportunity structures, and prosociality. Our contribution suggests the reason social ties with undocumented immigrants are not necessarily a hindrance to political engagement among Latinx immigrants and their co ethnics is because they can draw from identitarian resources to overcome participatory constraints.