Amid growing globalization, many countries have offered tax incentives to attract corporate investment. Prior research studies the role such incentives play in firms’ location and investment choices. However, we have limited evidence on the role that uncertainty about the intensity of future tax enforcement plays in those decisions. In 2013, the European Commission (“E.C.”) abruptly began investigating tax ruling practices of several countries in response to allegations that certain firms received preferential tax treatment (“state aid cases”). We use this setting to study the economic consequences of increased uncertainty about future tax enforcement. We find evidence consistent with significant reductions in U.S. multinational enterprises’ subsidiary investments within, firm input purchases from, and aggregate investment of U.S. firms flowing to targeted state aid countries. Specifically, for U.S. multinational enterprises’ subsidiary investments we find fixed assets declined by 1.7 percent of total assets, or $7.6 million per subsidiary.