Unions provide higher than competitive wages for members, but their effect on non-union wages is not clear. We investigate the effect of union density on supermarket wages from 1986 to 1993, a period of declining real wages and declining union membership. Full-information maximum likelihood techniques are used to estimate log wage equations for both the union and nonunion sectors. Decomposition techniques then separate the union wage premium into the relative effects of densities and union membership. We find a significant, positive effect of union density for both union and nonunion employees. This effect explains approximately one-third of the union-nonunion wage differential.