The theory of normative social behavior (TNSB) postulates that people are influenced by others' behaviors, which they observe from messages and experience. In addition to focusing on perceived (i.e., descriptive and injunctive) norms, the TNSB was expanded to include collective norms, which represent what people actually do. Testing this expanded theoretical model, the current study examined whether two types of collective norms - collective political norms and collective regional norms - interacted with descriptive norms to influence pandemic mask wearing behavior expectations among U.S. adults (N = 444). The interaction was statistically significant for collective political norms (β = -.74, p = .009) but not collective regional norms (β = -.16, p = .85). Specifically, descriptive norms were related to increased mask wearing expectation for all values of political party collective norms, but the effects were stronger when political party collective norms were low (i.e., low mask wearing behavior was normative). The findings support the inclusion of collective norms in the TNSB, clarify the relationships among different types of norms, and provide insights for norms-based interventions.