Labor market concentration can worsen after a merger takes place, and this heightened concentration can negatively affect wages. The focus of antitrust analysis, however, has been on the prices of consumer products, not the wages of laborers. New research indicates that, on average, labor markets are highly concentrated, and that higher concentration is associated with significantly lower posted wages for new jobs. This brief uses existing economic tools to develop a model for evaluating labor market concentration and its effects, to determine if a merger will run the risk of anticompetitively suppressing wages, employment, and output. Regulators can use this model to apply antitrust principles to labor markets, as a basis for antitrust enforcement.