Workplace safety policies are designed to ensure that employers internalize the costs of injuries, but employers can undermine these policies with threats of dismissal. We show that states' adoption of the public policy exception to at-will employment—an exception forbidding employers from firing workers for filing workers' compensation claims or for whistleblowing—led to a substantial reduction in injuries. The widespread adoption of the public policy exception explains 14 percent of the decline in fatal injury rates between 1979 and 1994. Statutory protections from retaliatory firing also improved safety, but only when employers faced sufficiently strong penalties for violating them.