The Federal Trade Commission (“FTC”) and U.S. Department of Justice Antitrust Division (“DOJ”) recently introduced proposed revisions to the existing merger guidelines. The new draft guidelines, if enacted in a form similar to the current draft, would represent a seismic shift in how the agencies approach antitrust merger investigations. They expand the types of transactions expected to result in additional scrutiny and lower the threshold for market shares that may be considered problematic. Ultimately, the new guidelines are likely to lead to additional merger challenges.