We measure the extent that a prevailing law can affect moral and social norms. We use variations in facemask fines in the UK during the COVID-19 pandemic as a case study, as it presents us with many features of a natural experiment. Our analysis provides two important findings. First, we find that the legal status of a behaviour, that is whether the behaviour is illegal or not, is important in influencing stated compliance and moral and social norms. In contrast we find no evidence that a variation in penalties has any effect on stated compliance or moral or social norms. We consider these results are important for law makers and society, as both moral and social norms are known to be important drivers of social change, and our results show that legality influences both—thus highlighting an endogenous relationship between the law—and moral and social norms.