Government agencies around the world struggle to retain frontline workers, as high job demands and low job resources contribute to persistently high rates of employee burnout. Although four decades of research have documented the predictors and potential costs of frontline worker burnout, we have limited causal evidence on strategies that reduce it. In this article, we report on a multi-city field experiment (n=536) aimed at increasing perceived social support and affirming belonging among 911 dispatchers. We find that a six-week intervention that prompts dispatchers to share advice anonymously and asynchronously with their peers in other cities reduces burnout by 8 points (0.4 SD) and cuts resignations by more than half (3.4 percentage points) four months after the intervention ended. We provide supporting evidence that the intervention operates by increasing perceived social support and belonging in an online laboratory experiment (n=497). These findings suggest that low-cost belonging affirmation techniques can reduce frontline worker burnout and help agencies retain workers, saving a mid-sized city at least $400,000 in personnel costs.