AimsTo explore illegitimate tasks as a potential mechanism that links permanent nurses' perceived exposure to temporary nurses to lower levels of affective organizational commitment.DesignA time‐lagged cross‐sectional survey study.MethodsSurvey data from N = 239 permanent nurses in the German‐speaking part of Switzerland were analysed via Structural Equation Models.ResultsThe study revealed a negative relationship between permanent nurses' perceived exposure to temporary nurses and their level of organizational commitment that was mediated by perceptions of unreasonable and unnecessary tasks.ConclusionHealthcare institutions increasingly depend on temporary nurses to fill staffing vacancies. Our data suggest that the deployment of temporary nurses may have adverse effects on permanent nurses' affective organizational commitment via perceptions of illegitimate tasks.ImpactOur quantitative survey study provides a novel, theory‐driven understanding of how perceived exposure to temporary nurses may impact work‐related attitudes of permanent nurses.Implications for the Profession and/or Patient CareOur findings suggest that the clinical community should limit permanent nurses' exposure to temporary nursing staff to protect their commitment. If this is not possible, we encourage strategies to counteract associated feelings of illegitimacy, for example, by showing appreciation for permanent nurses' willingness to take over responsibility for temporary nurses.Reporting MethodThe study adheres to the STROBE reporting guidelines for cross‐sectional studies.Patient or Public ContributionNo patient or public contribution.