When is paternalistic regulation of risky work justified, and who should get to decide that question? The prevailing economic account of OSHA regulation is that market interventions are justified only by spillover and informational market failures. This article challenges that prevailing account by contending that worker safety regulations are also justified where necessary to enforce the relational expectations of employees, which are shaped not only by formal contract but also by social norms and norms internal to the employment relationship. Drawing on the relational theory of contract, this article identifies an underappreciated purpose for employment law: anti-opportunism. If preventing relational opportunism is a valid purpose for workplace safety law, then OSHA regulation is justified in a broader range of circumstances than has been generally assumed under more traditional analyses. This article contends that regulation is justified where necessary to prevent employers from engaging in self-interested behavior that runs contrary to the parties’ relational expectations. Applying this standard is a highly context-specific, fact-dependent task, which makes Congress’ decision to delegate enforcement authority to OSHA appropriate.