Purpose: This paper investigates how organisations are responding to mandatory modern slavery disclosure legislation. Experimentalist governance suggests that organisations faced with disclosure requirements such as those contained in the UK Modern Slavery Act 2015 will compete with one another, and in doing so, improve compliance. The authors seek to understand whether this is the case. Design/methodology/approach: This study is set in the UK public sector. The authors conduct interviews with over 25% of UK universities that are within the scope of the UK Modern Slavery Act 2015 and examine their reporting and disclosure under that legislation. Findings: The authors find that, contrary to the logic of experimentalist governance, universities' disclosures as reflected in their modern slavery statements are persistently poor on detail, lack variation and have led to little meaningful action to tackle modern slavery. They show that this is due to a herding effect that results in universities responding as a sector rather than independently; a built-in incapacity to effectively manage supply chains; and insufficient attention to the issue at the board level. The authors also identity important boundary conditions of experimentalist governance. Research limitations/implications: The generalisability of the authors’ findings is restricted to the public sector. Practical implications: In contexts where disclosure under the UK Modern Slavery Act 2015 is not a core offering of the sector, and where competition is limited, there is little incentive to engage in a “race to the top” in terms of disclosure. As such, pro-forma compliance prevails and the effectiveness of disclosure as a tool to drive change in supply chains to safeguard workers is relatively ineffective. Instead, organisations must develop better knowledge of their supply chains and executives and a more critical eye for modern slavery to be combatted effectively. Accountants and their systems and skills can facilitate this development. Originality/value: This is the first investigation of the organisational processes and activities which underpin disclosures related to modern slavery disclosure legislation. This paper contributes to the accounting and disclosure modern slavery literature by investigating public sector organisations' processes, activities and responses to mandatory reporting legislation on modern slavery.</p