Should unions and corporations be treated identically under the antitrust laws? This article explores this provocative question by examining whether union mergers should be subject to the antitrust laws. Currently unions and corporations are treated very differently. Large corporate mergers are blocked if their effect may be substantially to lessen competition, or to tend to create a monopoly . They are permitted if they are likely to be benign, procompetitive, or proconsumer. Collective bargaining, by contrast, enjoys a broad exemption from the antitrust laws. If they follow appropriate procedures, unions - even unions that, when taken together, cover all workers within a given industry - are permitted to merge or to coordinate their acti...