How do powerful unions affect firms' debt maturity structure? I find that firms increase the fraction of long term debt as a response to unionization while keeping their leverage ratio unchanged. Using a regression discontinuity design I estimate that unionized firms increase by 25% the fraction of long-term debt as compared to union-free firms. I explore several channels consistent with a debt maturity structure reshaping rather than a strategic leverage increase. I find that financially constrained, less flexible, and small firms exploit the positive effects of union's monitoring activity to lengthen their maturity structure so that to reduce refinancing risks. My findings support the view that bond market values positively the presence of powerful non-financial stakeholders with aligned interests and incentives to monitor over the firm's policies.