This paper studies how imposing norms on contribution behavior affects individuals' intrinsic motivation. We consider the church levy, which the Catholic Church in Germany collects as a charitable donation, despite the fact that the levy is legally a tax. We design a randomized field experiment with treatments informing individuals that the levy is a tax. We demonstrate that treatment effects differ across motivational types. Among weakly intrinsically motivated individuals, communicating the legal norm results in a significant crowd-out of intrinsic motivation. In contrast, strongly intrinsically motivated individuals do not show any treatment response. (C) 2016 Elsevier B.V. All rights reserved.