To date, the emergence of representation of hitherto under-represented workers has mainly been analysed in terms of strategic choices of traditional industrial relations actors. This study – focused on solo self-employed workers (SSE) – instead analyses the interactions between unions, employer organisations and new collective actors, namely SSE associations. More specifically, drawing on a comparative ethnography conducted in three European countries, it conceptualises the representation of SSE as a ‘subfield’ of the ‘parent field’ of employee and employer representation and shows how interactions between traditional and new collective actors consolidate the subfield of SSE representation by also shaping the industrial relations’ institutions. This article thus contributes, first, to the debate about the representation of under-represented workers by emphasising the importance of interactions between traditional and new actors in industrial relations, and second, to the theory of fields by conceptualising interactions as a central element of field-level change.