Customer Concentration and the Upstream Propagation of Idiosyncratic Shocks: Evidence from Labor Strikes




This paper studies the role of customer concentration in the upstream propagation of idiosyncratic firm-level shocks. I utilize major labor strikes as idiosyncratic disruptions of large firms with multiple suppliers. I find that strike-hit customers impose a substantial output loss on their suppliers. The negative effect increases with suppliers’ direct dependence on disrupted customers. Moreover, suppliers’ output loss is amplified by additional indirect links that exist if suppliers sell products to other companies whose business also depends on the large disrupted customer. Overall, these results show that customer concentration increases the vulnerability of production networks to idiosyncratic firm-level shocks.