Labour commodification is a core process in building capitalist society. Nonetheless, it is given remarkably little attention in labour and social historiography, because assumptions about the process have obscured its historical character. Abandoning these assumptions, a close study of labour commodification in the boilermaking trades of late colonial New South Wales (Australia) illustrates the historical character of the process. In these trades, labour commodification was deeply contested at the most intimate level of class relations between workers and employers. This contest principally took the form of a struggle over the scheme of occupational classification used as the basis of pay rates. It was a highly protracted struggle, because workers developed strategies that kept the employers' efforts at bay for four decades. Employer efforts to intensify the commodity character of boilermakers' labour were largely ineffective, until they were given great assistance in the early twentieth century by the state arbitration system.