This paper investigates the role of the stock of unionized labor in determining equity investment risk. I estimate a labor stock measure based on expected compensation costs, and use the ratio of labor stock to total assets as a risk proxy. At the median, the labor stock is comparable in magnitude to total assets. Regression estimates show the associations between labor-based risk proxies and equity market risk measures are both economically and statistically significant. In addition, the labor-based measures provide risk information over and above information contained in standard risk proxies such as financial and operating leverage.