Existing research has found heterogeneity in the implementation of Lean and its outcomes in terms of employee involvement across countries. This article explores the potential role of labour–management relations. It relies on in-depth company case studies carried out in the aerospace industry in France and Sweden. The study finds significant variations in employee involvement – higher in the Swedish than in the French cases. Managerial orientations did play a role, as the ‘technocratic’ form of Lean in France echoed a more unilateral top-down conception of management, while Swedish managers appeared more receptive to the ‘involvement-enhancing’ paradigm. But the attitudes and behaviours of unions were also a crucial factor, as Swedish unions were very effective in impinging on the implementation of Lean at workplace level, while their French counterparts, often divided, adopted a more defensive stance, lacking expertise and implication in the promotion of high-involvement work organisations.