PurposePossible asymmetric treatment among family members has long been neglected in the field of family firm research. To fill this gap, the purpose of this study is to shed light on the heterogeneity of treatment of family members in family firms by proposing factors that influence the likelihood of bifurcation bias among “family” members.Design/methodology/approachDrawing upon social identity theory and the concept of bifurcation bias, the authors theorize that family members working in family firms are not a homogenous entity, but rather a heterogeneous entity contingent on their status and/or position in the family. To provide a comprehensive understanding of heterogeneous treatment among family members, both individual factors and societal factors should be considered.FindingsBlood relatedness of family members is suggested as an important determinant of the likelihood of bifurcation bias among family members. It is also proposed that the impact of blood relatedness is likely influenced by both individual factors (familial proximity and familial tenure) and a societal factor (collectivism).Originality/valueTheorizing takes a step forward to advance the understanding of interpersonal dynamics in family firms. In particular, this article expands the research boundaries of family business research by taking into account that not all “family” members are treated preferentially. Moreover, this article deepens our understanding of the nature and status of non-blood related family members by unveiling the influence of both individual and societal factors. This article also provides a theoretical foundation for human resource management (HRM) research in family businesses by addressing bifurcation bias among family members.