Abstract: The authors examine enterprise-level antecedents of wildcat strikes in Vietnam using a national representative sample of foreign-invested enterprises over the period 2010 to 2012, coding of factory audits, and field research. They predict that these unauthorized, semi-spontaneous work stoppages are more common among unionized workplaces, because the presence of a union in the workplace signals to workers that by engaging in a wildcat strike, they may be able to activate the representation and protection role of official trade unions. That is, workers can in some cases push unions from below to act on their behalf. In addition, wholly foreign-owned enterprises, investments by Asian-owned firms, and manufacturing operations in industrial zones are associated with more strikes than are joint ventures with state-owned and private enterprises, firms owned by Western investors, and firms in higher-value-added activities. Statistical results and field research provide strong support for these predictions. These findings suggest that the role of trade unions in socialist states may be more nuanced than previously assumed. At the same time, they reinforce the observation in the literature that Vietnamese employment relations institutions are unable, in and of themselves, to address worker grievances.