Criticism of neoliberal globalisation has become associated with xenophobia, racism and nationalism, enabling far-right populist demagogues such as Marine Le Pen and Donald Trump to exploit working-class discontent with globalisation. Yet less than two decades ago a radical left-wing movement was seriously challenging globalisation and demonstrating that critique of corporate globalisation was compatible with internationalism and working-class solidarity across national borders. Where was labour in this important movement? Did unions participate in blockading the citadels of corporate power? Evidence from case studies of four mobilisations (Seattle November-December 1999, Melbourne September 2000, Québec City April 2001 and Genoa July 2001) suggests strong working-class involvement, especially of white-collar workers from the public sector, and important contributions from union activists and particular radical unions as organisations. However, trade union officials often preferred union contingents keep a safe distance from centres of action. Significant conflicts were apparent within unions between class-conscious activists, who wished to embrace the growing left-wing movement against globalisation, and more conservative officials. It confirmed the truism of union movement scholarship: the problem of full-time bureaucracies with interests distinct from those of rank-and-file workers; and the existence of the “universal tension” between the contradictory elements of “movement” and “organisation.” Ambivalence and prevarication did not present the union movement in the best possible light to workers angry and distressed by the effects of globalisation. Did the hesitant role played by unions in alter-globalisation campaigns contribute to union decline and prepare the ground for right-wing populist opposition to globalisation? Was this a lost moment for labour?