A common dilemma in regulation is determining how much trust authorities can place in people's self-reports, especially in regulatory contexts where the incentive to cheat is very high.In such contexts, regulators, who are typically risk averse, do not readily confer trust, resulting worldwide in excessive requirements when applying for permits, licenses, and the like. Studies in behavioral ethics have suggested that asking people to ex-ante pledge to behave ethically can reduce their level of dishonesty and noncompliance. However, pledges might also backfire by allowing more people to cheat with no real sanctions. Additionally, pledges' effects have only been studied in one-shot decision making, and they may only have a short-term effect that could decay in the long run, leading to an overall erosion of trust. We explored the interaction of pledges with sanctions and the decay of their effects on people's honesty by manipulating whether pledges were accompanied by sanctions (fines) and testing their impact on sequential, repeated ethical decisions. We found that pledges considerably and consistently reduced dishonesty, and this effect was not crowded out by the presence of fines. Furthermore, pledges seem to exert an effect on most people, including those who are relatively less inclined to follow rules and norms. We conclude that pledges could be an effective tool for the behavioral regulation of dishonesty, reduce the regulatory burden, and build a more trusting relationship between government and the public, even in areas where incentives and opportunities to cheat are high.