During the COVID-19 pandemic, the CDC and the WHO have recommended face masks as key to reducing viral transmission. Yet, in the USA, as the first wave erupted in the Summer of 2020, one-fifth of individuals said they wore masks at most “some of the time”, and a majority said that people in their community wore masks at most “some of the time”. What strategies most effectively encourage compliance with this critical COVID-19 prevention measure? Relying on social identity theory, we experimentally assess two possible mechanisms of compliance, elite endorsement, and social norms, among a representative sample of white US-born Evangelicals, a group that has shown resistance to prevention measures. We find evidence for both mechanisms, but social norms play a remarkably important role – increasing support for mask-wearing by 6% with spillover effects on other prevention guidelines. Our findings confirm the role that appeals to norms and elite endorsements play in shaping individual behavior and offer lessons for public health messaging.