Recently, Finnish forest industries shifted from sectoral collective bargaining to firm‐level bargaining, and the IT services industry shifted to a hybrid of sector‐ and firm‐level bargaining. Using administrative data on monthly wages and the synthetic difference‐in‐differences method, I study the causal effects of collective bargaining decentralization on the level and dispersion of wages. Despite the substantial change in the level of collective bargaining, I generally find muted effects on the level and dispersion of wages. I find positive and economically and statistically significant effects on wage levels and within‐firm wage dispersion only for blue‐collar workers in the paper industry.