This paper proposes a theoretical and quantitative analysis of the reallocation of labor across firms in response to idiosyncratic shocks of different persistence. Creating and destroying jobs is costly and workers are paid a share of the value of the marginal worker. The model predicts that employment and labor costs react differently to transitory shocks and permanent shocks. Quantitative evaluation of the model on a panel of French firms shows the model’s performance. Modest adjustment costs are needed to reproduce observed job reallocation and inaction rates. Removing adjustment costs leads to productivity gains of 1% at the steady state. These gains are 50% larger in a economy with only transitory shocks and an order of magnitude lower in an economy with only permanent shocks. Bargaining dampens the reallocation of labor across firms, leading to larger efficiency losses from adjustment costs.