Stealth Consolidation: Evidence from an Amendment to the Hart-Scott-Rodino Act

Prospective merger review is the most frequent application of antitrust law. It exempts transactions on the basis of size, though small deals can have large anticompetitive effects in segmented industries. I examine its impact on antitrust enforcement and merger activity in the context of an abrupt increase in the US exemption threshold. I find that among newly-exempt deals, antitrust investigations fall to almost zero while mergers between competitors rise sharply. Effectively all of the rise reflects an endogenous response of firms to reduced premerger scrutiny, consistent with large deterrent effects of antitrust enforcement.