We use 1080 bonds and notes issued between 1993 and 2010 in US markets as our sample, and model the two-stage least squares regression to investigate the impact of union strength on the term to maturity. Controlling for previously identified determinates of debt maturity and modeling leverage and debt maturity as jointly endogenous, we find a significant and positive relation between union strength and the term to maturity. Firms under high union strength are likely to issue debts with longer term to maturity. In addition, the impact of union strength on the term to maturity would be affected by the situation of the firm. More profitability, less default risk or current assets increased would increase the impact of union strength on the term to maturity.