This study examines the impact of unionized labor on supermarket performance, as measured by profit and sales, accounting for the competitive presence of supercenters. The results confirm prior research that shows that supercenters have negative effects on supermarket performance. Unionized supermarkets generally outperform nonunionized supermarkets. However this effect disappears when accounting for supercenters, largely because unionized stores are less likely to compete with supercenters. I find no evidence for a significant union effect on supermarket performance. The deleterious effects of supercenters are stronger for unionized stores. Unionized supermarkets utilize less full-time labor and more labor-saving technology than do nonunionized ones.