Many countries use TV licence fees to finance public broadcasting. The system is susceptible to free riding since enforcement measures are weak and public broadcasting programs can be received without paying. Public agencies detect households who evade license fees and contact them through mailings. In a natural field experiment we vary the messages of these letters. We implement a legal threat - stressing the legal consequences of detected evasion - social information - pointing out the actual level of compliance - and a moral appeal to fair compliance behavior. In total, we sent 48.000 mailings in six different treatments. An additional control group did not receive any mailing. We find that all mailings strongly increase the number of new registrations as compared to the control. Within the mailing treatments, the legal threat proves to be most successful. The social information shows a positive impact only among those who expected compliance to be lower than stated. This last result suggests that beliefe management represents an alternative enforcement policy.