We run a large-scale natural field experiment to evaluate alternative strategies to enforce compliance with the law. The experiment varies the text of mailings sent to potential evaders of TV license fees. We find a strong effect of mailings, leading to a substantial increase in compliance. Among different mailings, a threat treatment which makes a high detection risk salient has a significant deterrent effect. Neither appealing to morals nor imparting information about others' behavior enhances compliance on aggregate. However, the information condition has a weak positive effect in municipalities where evasion is believed to be common. (authors' abstract)