This report examines whether and how co-enforcement-notably the collaboration between labour inspectors and trade unions-can narrow Europe's widening enforcement gap amid fissured workplaces and rising precarity. We study Germany, Italy and Poland through a systematic review of scientific and grey literature and ten expert interviews. We show that enforcement remains siloed: in Germany, cooperation clusters around wage monitoring and migrant exploitation with limited feedback to workers; in Italy, integration under the National Labour Inspectorate is uneven across regions; in Poland, a strong legal mandate is undermined by civil law contracting, low fines and resource constraints. Across cases, co-enforcement tends to reach organised segments while bypassing the most precarious workers. Yet evidence shows worker voice 1 and union presence improve complaint-based inspections and targeting. We argue that effective co-enforcement requires (i) strategic focus on high-risk sectors, (ii) institutionalised participation of workers-protected whistleblowing, advice centres embedded in enforcement, and systematic feedback loops-and (iii) transnational coordination that mirrors cross-border subcontracting. Moving beyond "light-touch" compliance, inspectorates need adequate staffing, legal prerogatives and data integration to deter non-compliance. Co-enforcement is not a bureaucratic add-on but a power strategy that mobilises workers' knowledge to close the enforcement gap.