Considering that the members of the International Non-Governmental Organizations (INGO) Accountability Charter played a prominent role in initiating the first sector supplement of the Global Reporting Initiative for non-governmental organizations (NGO), the purpose of the paper is to investigate their sustainability reporting (SR) practices in order to evaluate to what extent INGO Charter members comply with this voluntary accountability standard for SR. The empirical analysis is based on a content analysis of sustainability reports. The findings indicate that most of the INGO Charter members are far away from a comprehensive reporting practice. Hence, critical voices could assert that their reporting behavior seems to be more in line with facade building than the idea of providing a comprehensive account. By adapting a multiperspective theoretical discourse about the potential and shortcomings of SR to the NGO context, the study contributes to a field-specific theory-based pluralistic critical evaluation of SR as a major cross-sectoral innovation in voluntary accountability initiatives.