One of the most important problems in Latin American Urban Anthropology, is the fact that most of Latin American cities were founded and grew due to the needs of colonial governments and/or the demands for the exchange of products between those cities and the countryside. As a consequence, the existence of an urban working class -the most important social group in western cities during the past century- capable to exert an important influence on the process of urbanization in Latin America has been scarcely documented. This article deals with a city whose history has been linked, since its origins, to the needs of the industrial sector and where development has been greatly influenced by the urban working class and its trade unión.