Does mandatory shareholder voting prevent bad acquisitions?

Shareholder voting on corporate acquisitions is controversial. In most countries, acquisition decisions are delegated to boards, and shareholder approval is discretionary, which makes existing empirical studies inconclusive. We study the U.K. setting in which shareholder approval is imposed exogenously via a threshold test that provides strong identification. U.K. shareholders gain 8 cents per dollar at announcement with mandatory voting, or $13.6 billion over 1992–2010 in aggregate; without voting, U.K. shareholders lost $3 billion. Multidimensional regression discontinuity analysis supports a causal interpretation. The evidence suggests that mandatory voting imposes a binding constraint on acquirer chief executive officers.