Purpose Employee reward is central to contemporary debates about work and employment relations; and in the context of ongoing wage stagnation, benefits represent a growing proportion of total reward value. Past studies have shown that when employees perceive benefits as unfair, this has a negative impact on engagement, performance and retention. Yet no previous studies have explored the components of a benefits system that influence employees' fairness concerns. Using organisational justice as a theoretical lens, the purpose of this paper is to examine how dimensions of an employee benefits system influence the fairness perceptions of employees. Design/methodology/approach This paper reports on a qualitative, inductive case study of the benefits system in a large finance and insurance company, drawing on three data sources: interviews with the company's benefits managers, organisational documents and open-text responses from a benefits survey. Findings Three dimensions of the benefits system strongly influenced fairness perceptions - constraints on accessing and utilising benefits; prosocial perceptions about the fairness of benefits to third parties; and the transparency of employee benefits. Originality/value This study makes a conceptual contribution to the benefits literature through a detailed exploration of the type of organisational justice judgements that employees make about benefits; and identifying for the first time prosocial fairness concerns about the impact of benefits on third parties.