Purpose: This paper aims to provide empirical evidence on formal stakeholder participation (or “lobbying”) in the early phase of the International Sustainability Standards Board’s (ISSB’s) standard-setting. Design/methodology/approach: Drawing on a rational-choice framework, this paper conducts a content analysis of comment letters (CLs) submitted to the ISSB in response to its first two exposure drafts (published in 2022) to investigate stakeholder participation across different groups and jurisdictional origins. The analyses examine participation in terms of frequency (measured using the number of participating stakeholders) and intensity (measured using the length of CLs). Findings: Preparers and users of sustainability reports emerge as the largest participating stakeholder groups, while the accounting/sustainability profession participates with high average intensity. Surprisingly, preparers do not outweigh users in terms of participation frequency and intensity; and large preparers outweigh smaller ones in terms of participation intensity but not participation frequency. Internationally, stakeholders from countries with a private financial accounting standard-setting system participate more frequently and intensively than others. In addition, country-level economic wealth and sustainability performance are positively associated with more participating stakeholders. Practical implications: This study is of interest for organizations and stakeholders involved in or affected by standard-setting in the field of sustainability reporting. The finding of limited participation by investors and from developing countries suggests the ISSB take actions to enhance the voice of those stakeholders. Social implications: The imbalances in stakeholder participation that were found pose potential threats to an important aspect of the input legitimacy of the ISSB’s standard-setting process. Originality/value: To the best of the authors’ knowledge, this paper is the first to explore stakeholder participation by means of CLs with the ISSB in terms of frequency and intensity.