This study presents an exploratory analysis on the factors influencing various behavioral patterns of union members' participation. The existing literature hardly provides comprehensive examination over the different mobilizing level of union members, while largely focusing on the empirical analysis of particular union-related behavioral categories, such as union affiliation and strike attitude. To fill in the research vacuum, we compare three analytical models concerning different union participation patterns, including low-risk participation, high-risk participation, and union withdrawal, by drawing on the 8th Korea Labor & Income Panel Survey data. Our analysis reveals the differing causal mechanism among various union participation patterns. The study finds that the public function of labor unions, measured by their socio-economic roles and public representation, is a key factor to lead union members to participate to various union activities and stay in the labor union. Another finding is that the union's instrumental function for improving employment conditions is positively correlated with low-risk union participation and organizational retention, whereas cooperative industrial relations are likely to promote high-risk union participation and organizational retention. Finally, workplace discontent has a significant impact on union withdrawal, which implies that the union's shopfloor representation to resolve workers' concerns is critical for the retention of its membership.