Purpose
The purpose of this study is to provide new insight into the modern slavery threat and to enhance its detection in supply chains by understanding and addressing barriers to whistleblowing. A broad definition of a whistle-blower is adopted, which includes any witness internal or external to an organisation.

Design/methodology/approach
This is a viewpoint paper that includes using news reports and other secondary data sources on a recent modern slavery scandal in garment factories in Leicester, UK and the lens of the bystander effect from the social psychology literature. The core focus is on whistleblowing by members of the local community in which an operation or supply chain is embedded.

Findings
The phenomenon of modern slavery being an “open secret” within the local community is highlighted. But rather than the case being characterised by widespread whistleblowing, the problem only came into full focus when poor working conditions and forced labour during COVID-19 lockdown restrictions contributed to the spread of the virus. It is argued that overcoming this “bystander effect” can lead to the greater mobilisation of modern slavery whistleblowing.

Research limitations/implications
Two sets of propositions and a conceptual model are provided and seven future research suggestions are outlined, including extending the present study to whistleblowing by victims and other internal members of an organisation or supply chain.

Practical implications
If it can be mobilised, then whistleblowing has the potential to be an important part of detecting modern slavery, either temporarily replacing audits where they are not possible due to social distancing restrictions or directing the use of limited auditing resources to high-risk factories. In this way, combinations of practices can be effectively used to tackle the threat.

Social implications
This contributes to addressing an important societal problem and one of the grandest challenges facing modern-day supply chains. This, it has been argued, is an even bigger problem now than ever before given the economic and market conditions created by the COVID-19 global pandemic.

Originality/value
This is the first paper to focus on operationalising the practice of whistleblowing as a source of greater supply chain intelligence to aid modern slavery detection. Causes of the bystander effect include the perceived low-emergency threat of modern slavery, the high-ambiguity environment, a low bystander responsibility and low assistance/intervention incentive. Countermeasures include elevating the emergency status of modern slavery, creating a shared sense of responsibility for tackling the problem, having clear reporting channels and taking swift and consistent action when instances of modern slavery are detected.