Purpose The purpose of this paper is to investigate whether and how knowledge hoarding, functions as antecedent and consequent of work related negative acts, as a measure of bullying. The authors investigate the relation as mediated by trust and justice. Design/methodology/approach Data stem from a longitudinal study in which questionnaire responses were collected twice from 1,650 employees in 52 workplaces. Structural equation modelling was used to analyse the two models. Design-based corrections were made to accommodate the multi-level structure of data. Findings The analyses showed that knowledge hoarding was both an antecedent and a consequent of negative acts. First, over time, knowledge hoarding was indirectly related to negative acts mediated by trust and justice. Second, negative acts were both directly and indirectly related to knowledge hoarding over time. The study thus points to the existence of a vicious circle of negative acts, psychological states of trust and justice, and knowledge hoarding behaviours, which presumably will affect both individual and organizational outcomes negatively. Research limitations/implications The use of already collected, self-report data, single-item measures, and the two-year time lag could pose potential limitations to the study. Practical implications Preventive and repair actions could potentially impact both negative acts and knowledge hoarding by focusing on increasing the social exchange quality at work unit level. Originality/value This paper combines two strands of research, that of bullying at work and that of knowledge management, within which research on knowledge hoarding has been an under-researched area.