This Master’s thesis analyses how the introduction of mandatory extension of collective agreements in 2004 affected the union density rate in Norway. By using the synthetic control method, the effect of mandatory extension on union density is calculated by estimating how the union density in Norway would have developed, if mandatory extension of collective agreements were never introduced. The results indicate that mandatory extension of collective agreements has had a positive effect on union density, but they are not significant. There is, however, nothing in the results to indicate that mandatory extension has had a negative effect on union density.
