Illegitimate tasks violate the norms of what is considered part of the employee's work role and have been found to harm individuals, groups and organisations. The purpose of this study was to investigate the relationship between key organisational conditions - span of control, recruitment needs, administrative support and organisational changes - and the prevalence of unnecessary and unreasonable illegitimate tasks experienced by managers and their subordinates. Data were collected from a sample comprising 80 managers and 863 subordinates in a Swedish municipality using questionnaires to assess their perceptions of illegitimate tasks. Organisational conditions were collected from the human resources register in the municipality. Multilevel analysis results reveal a positive association between the size of workgroups and illegitimate tasks; the more subordinates per workgroup, the more unnecessary and unreasonable tasks managers reported and the more unreasonable tasks the subordinates reported. These findings hold practical implications for organisations because they indicate that illegitimate tasks can be reduced by decreasing the number of employees in larger workgroups.