Dispute resolution by third parties is a cornerstone of national industrial relations systems across Europe. However, the formal powers of the institutions of conciliation, mediation and arbitration vary considerably across countries. I aim to explain the existence of strong third-party intervention across 17 Western European countries, using fuzzy-set qualitative comparative analysis. I test two hypotheses: first, that strong institutions are established to control collective bargaining when unions are powerful but fragmented; second, that strong institutions reflect legal traditions that use civil courts rather than specialized labour courts. The analysis supports the first hypothesis but not the second. Recent reforms since the Great Recession in Southern European countries further corroborate this finding.