An unintended consequence of mass imprisonment is the growth of prison officer unions. This article shows how successful corrections unions in states like California and New York obstruct efforts to implement sentencing reforms, shutter prisons, and slash corrections budgets. They impede downsizing-oriented reforms by generating or exacerbating fear among voters and politicians. Policy makers in key states must overcome resistance from prison officer unions to downscale prisons. Through a combination of accommodation and confrontation, policy makers can relax opposition from the officer organizations and undertake prison downsizing efforts without busting the unions.