This paper derives, and then estimates, a model of employment where unions and firms bargain over wages and possibly employment, and efficiency wage considerations may be important. It illustrates the difficulties associated in interpreting many existing attempts to discriminate between alternative models. The results (based on over 200 U.K. firms) suggest that employment is negatively related to the firm's own wage and the change in the own wage relative to outside opportunities. The latter may be an efficiency wage effect. Various financial factors are also seen to have a significant effect on employment.