This analysis extends theoretical models of ethnic boundary formation to account for the shifting and layered nature of ethnic boundaries. It focuses on the underlying structural conditions that facilitate the expansion ofethnic boundaries or the construction of a pan-national identity, and explores how organizing along an ethnic boundary affects collective efforts at the panethnic level. Two processes could be occurring: (I) Competition with other ethnic or racial groups could lead groups with different national origins to engage in collective action based on a pan-national boundary, or (2) occupational segregation could foster pan-national interests and networks that lead groups to participate in pan-national collective action. Using a new longitudinal data set ofcollective action events involving Asian Americans, the analyses indicate that the segregation ofAsians as a group raises the frequency of pan-national collective action, while the segregation among Asian subgroups depresses the rate ofpan-Asian collective action. The results also show that intragroup competition discourages pan-Asian collective action, and organizing along ethnic lines generally facilitates it. Overall, these findings are consistent with the cultural division oflabor theory, which suggests that segregation processes influence panethnic collective action due to intragroup interaction, common economic interests, and membership in a community of fate.