In order to reduce the shadow economy, the Hungarian government introduced mandatory online cash registers (OCR). In our research we use micro level data to estimate the effect of OCR introduction on reported turnover in the most affected sectors: retail, and accommodation and food services (AFS). For small enterprises, reported turnover increased by 23 percent and 35.1 percent in the retail and AFS sector, respectively. We also find significant but smaller effects for medium-sized enterprises in both sectors. For large companies, we only observe a significant impact in the AFS sector.