Empirical wage spillovers are often observed, but their theoretical explanation is controversial because they are consistent with institutional wage comparisons stemming from fairness or union politics, but also with neoclassical alternative wages or correlated labor demand shocks. The nature of wage spillovers is analyzed using a data set of United Automobile, Aerospace, and Agricultural Implement Workers of America (UAW) wage settlements, The results support the hypothesis that institutional wage spillovers augment neoclassical economic forces in determining wages, albeit with some weakening after 1980.