This article studies how participation norms affect workers’ willingness to strike. A factor analysis on the responses of 468 Dutch union members about appropriate behavior during a strike produces two factors. The first factor reflects a “solidarity norm” favoring group solidarity; the second factor reflects a norm about the treatment of defecting colleagues, which we call the “free-rider-punishment” norm. Using OLS regression, we show that adherence to these norms significantly affects union members’ willingness to strike, controlling for group identification, and past participation in strikes. This article contributes to a deeper understanding of how solidarity and free-rider-punishment affect future participation.