Many economists argue that state right-to-work laws, by disallowing union shops, encourage free riding and thus diminish union viability. Others counter that right-to-work laws are not enforced and that they represent local attitudes and employee characteristics which would encourage free riding in any me. We find that when other factors which affect free riding are taken into account, the marginal impact of right-to-work laws remains significant, although of a smaller magnitude than that found in previous bivariate studies.