We investigate to what extent workplace unionization protects workers from external shocks by preventing involuntary job separations. Using the COVID-19 pandemic as a plausibly exogenous shock hitting the whole economy, we compare workers who worked in unionized and non-unionized workplaces directly before the pandemic in a difference-in-differences framework. We find that unionized workers were substantially more likely to remain working for their pre-COVID employer and to be in employment. This greater employment stability was not traded off against lower working hours or labor income.