The purpose of this study is to provide a theoretical and doctrinal analysis of two variants of established practice as instruments for strengthening legal certainty in labour law. The analysis is comparative in nature and aims to identify both similarities and differences between these variants, as well as to demonstrate their potential for supporting the protective function of labour law. First, the paper examines custom and customary law within the workplace communi­ty. It then analyses labour-law interpretation “binding” by consensus as an analogous, though differently structured, mechanism of stabilization. Although the latter phenome­non occurs across various branches of law, its examination in the context of labour law appears particularly valuable in light of the specific features of this field and the special role that legal certainty plays for the parties to the employ­ment relationship. The autonomy of legal dogmatics entails that the modes of argumentation and justification under­lying the “binding force” of interpretation differ depend­ing on the branch of law concerned. Intuitions regarding the “binding” nature of interpretation arise differently in criminal or tax law than they do in labour or civil law. The analysis undertaken in this study may therefore serve as a useful point of departure for more detailed inquiries into the requirements of legal certainty for the parties to the em­ployment relationship.