The purpose of the article is to determine how the quality of interpersonal relationships at work (QIRW) affects the extent of counterproductive work behavior (CWB), and whether this impact is moderated by employees' demographic features (education, age, sex, length of service and type of work). These questions are particularly important for organizations that want to function sustainably, because counterproductive behavior also includes wasting resources, polluting the environment and using environmentally unfriendly products. The research objectives were met using a survey conducted in 2018 among 1488 professionally active people in Poland. Structural equation modeling (SEM) was used to analyze the empirical data. The proposed theoretical model was intended to determine how particular categories of relationship quality affect dimensions of CWB (which included taking into account employees' aforementioned demographic features). I determined that relationship quality has an inverse relationship with counterproductive behavior of employees (the higher the quality, the lower the propensity for CWB), but there are also many paradoxes that I discuss in detail. Moreover, this impact is significantly moderated by employees' demographic features (mainly education, type of work, length of service and sex). I also discuss the theoretical contributions, practical implications and limitations of this study, and directions for future research.Sustainability 2019, 11, 5916 2 of 33 which high-quality work relationships increase the propensity for counterproductive behavior directed against a person. This can be explained by the fact that such relationships are characterized by more frequent interaction and higher trust, which provides more opportunities for abuse [16]. The research issue is thus very complex and is strongly influenced by situational conditions and the features of the employees themselves.Thus far, the understanding of this relationship has tended to be based on intuition, and on research results that are scant at best, and that have been later cited by other authors as empirically confirmed paradigms [17]. The empirical studies on this topic are not comprehensive and focus on selected aspects of the impact of QIRW on CWB. For example: Skarlicki and Folger [18] investigated the impact of relationship quality on employee retaliation; Brass et al. [16] analyzed the impact of relationship quality on conspiracy; and Roberts [19] focused on the importance of relationship quality on, among others, work avoidance, the defensive behavior of personnel or the tendency to recognize one's own mistakes and to accept criticism. In turn, based on a meta-analysis of 161 articles, Chiaburu and Harrison [20] concluded that antagonisms between employees correlate negatively with job satisfaction, commitment and performance, and positively with absenteeism, the desire to leave work, staff turnover and CWB. Ragins and Verbos [21] also indicated a positive relationship between low relationship quality (understood as the exploitation...