ABSTRACT We examined the role of shop stewards’ union citizenship behaviours in the transmission of their attitude of union loyalty to rank-and-file union members. We hypothesized that union members (N = 1138) assimilate shop stewards’ (N = 312) union loyalty by observing their participation behaviours. Data on shop stewards´ union behaviours were both self-reported and informed by union members. The results from multilevel analyses confirmed that leaders’ union loyalty was positively associated with union members’ loyalty. In addition, the relation between shop stewards and union members’ loyalty was fully mediated by members’ perceptions of shop stewards’ participation. The practical and theoretical implications of this study are discussed.