Sustainability reporting has been increasingly criticized and especially legitimacy and accountability of the reports are questioned. Although the legitimacy of sustainability reports is questioned, it has not been studied further how stakeholders construct the legitimacy of the reports. We study stakeholders’ views on sustainability reporting by applying social contract theory and ask what legitimate sustainability reporting should consist of. We interviewed representatives of internal and external stakeholders of two Finnish companies on the usability and problems of sustainability reporting. Our aim is to identify how the interviewees construct different principles of legitimate sustainability reporting that would contribute social contract. We identified three different types of the principles for legitimate sustainability reporting: practicality, equivalence and target group specific reporting. To conclude, from the point of view of social contract theory, the sustainability reports in these contexts seem to fail to fulfill the requirements of expected openness and interaction between the company and the society. The main reason seems to be that sustainability reports were subjective publications, produced by companies to communicate on the issues they themselves wish to communicate and the actual stakeholder interests were not identified or met. This study contributes to the research of stakeholder relations and sustainability reporting by showing how internal and external stakeholder representatives expect sustainability reports to contribute to socially constructed contracts.