Despite the increasing recognition of data protection rights across the European Union (EU), evidence suggests they are often underenforced, thereby undermining the effectiveness of the General Data Protection Regulation (GDPR). This article shows that an often neglected aspect in GDPR enforcement is the variability in transparency exhibited by data protection authorities across EU Member States concerning the disclosure of fines. To bridge this research gap, we gathered data from 23 out of 27 EU data protection authorities (DPAs) and built an indicator to measure their level and quality of fines' disclosure. Our research uncovers disparities in the disclosure of GDPR fines across the EU. We examine the consequences of different levels of disclosure for individuals, entities, regulatory authorities and the data protection system. We argue that harmonised standards of transparency are necessary to ensure the effectiveness of the GDPR and the fundamental right to data protection across the EU.