Abstract: This study explores the effects of mental load and emotional load on counterproductive work behavior (CWB). Building on the conservation of resources theory and the challenge–hindrance stressor framework, we hypothesize that mental load enhances the effort and engagement of employees to accomplish goals and subsequently reduces organizational deviance (e. g., working time fraud), while emotional load, through resource depletion, weakens this relationship. We also suggest that by depleting emotional resources, emotional load could increase interpersonal deviance, with mental load exacerbating this effect due to synergistic effects. The results of a two-wave survey among 303 UK employees show that mental load reduces organizational deviance only when emotional load is low to moderate; when emotional load is high, mental load may even increase organizational deviance. The results also show that emotional load increases interpersonal deviance, irrespective of the level of mental load. The findings underscore the distinct nature of interpersonal and organizational deviance, challenges previous interpretations of the relationship between workplace stressors and CWB, and highlights the importance of considering the complex interplay between different types of stressors in predicting workplace outcomes.