Previous studies have shown that the most significant impacts of companies' operations are found in their supply chains, which are generally made up of small and medium-sized enterprises (SMEs). On the other hand, sustainability reporting is a vital tool for identifying companies' potential social and environmental impacts. It is also a critical factor that can help reduce risk and increase small businesses' competitiveness, facilitating their access to global value chains. However, the vast majority of research to date has focused on sustainability reporting by large multinational companies. In this context, this article's objectives are to broaden the debate on sustainable supply chain management and gain insight into the relationship between sustainability and competitiveness in companies. A qualitative approach is used through a case study method to investigate the Corporate Sustainability and Reporting for Competitive Business program in Peru. A sample of 72 SMEs from more than 20 sectors was analysed. The results show that the social dimension was the most reported with 52%, followed by environmental with 27% and economical with 21%. The sectors reporting the most are energy, textile, and logistics. The study also indicates that 78% of SMEs fully or partially met sustainability reporting requirements stipulated by lead companies. The program also enabled the companies to improve their strategic vision, strengthen the relationship with their respective leading companies, generate greater competitiveness, and access new markets. The main conclusions indicate academic and practical implications that will reduce the impact of operations and production on the supply chain and contribute to sustainable development. Finally, the study recommends future lines of research and the application of other methodologies.