PurposeThe purpose of this paper is to investigate the relationship between union practices and two types of employees’ extra-role behaviors, namely, union citizenship behavior (UCB) and employee voice (EV), and the mechanisms that mediate this relationship.Design/methodology/approachUsing matched data from 46 union leaders and 279 union members of 33 workplaces in China, this study utilized multilevel structural equation modeling to test the cross-level influences of union practices on employees’ extra-role behaviors and the mediation effects.FindingsThe results show that (1) union practices have a positive impact on employees’ UCB and EV, and (2) union practices increase UCB and EV through the improvement of industrial relations (IR) climate at the workplace level, as well as union commitment (UC) and union instrumentality (UI) at the individual level.Research limitations/implicationsAlthough the authors collected data from multi-sources (i.e. union leaders and members), the cross-sectional data of this study limited the ability to make casual inferences.Originality/valueThis study contributes to the literature by providing theoretical explanation and empirical evidence to illustrate the role of union practices in increasing the extra-role behaviors of employees (i.e. UCB and EV). This is of particular importance in elaborating the effectiveness of enterprise unions under the recent reforms in China. In addition, the authors also unpacked the antecedents of extra-role behaviors in the union context by investigating how IR climate, UC and UI mediate the relationship between union practices and extra-role behaviors of employees.