The Protocol and the Agreement on Social Policy annexed to the Treaty on European Union (the so‐called ‘social protocol’) stipulated the procedural rules of the European system of industrial relations about twenty years ago. It has been pointed out, however, that the procedure has such distinct features as centricity of cross‐sectoral agreements and a close nexus between legislation and negotiations, which most of the national social systems lack. This article locates the origins of these features in the historical processes towards the 1991 social partners' agreement through some primary and secondary documents as well as a series of structured questionnaire studies and hearings. It is discussed that, contrary to what some conventional interpretations assume, the social protocol was an original model of horizontal subsidiarity, with actors' different preferences on the desirability of labour market order governed by both legislation and negotiations in its background.