Regular church attendance is strongly associated with a higher probability of voting. It is an open question as to whether this association, which has been confirmed in numerous surveys, is causal. The repeal of the laws restricting Sunday retail activity (‘blue laws’) is used to measure the effects of church-going on political participation. Blue laws’ repeal caused a 5 percent decrease in church attendance. Its effect on political participation was measured and it was found that, following the repeal, turnout fell by approximately 1 percentage point. This decline in turnout is consistent with the large effect of church attendance on turnout reported in the literature, and suggests that church attendance may have a significant causal effect on voter turnout.