This article is a study of union effectiveness in an emerging market context. Mobilisation theory suggests that trade union power is based on rank-and-file notions of relative deprivation. Based on a survey of membership perceptions, we found that many of the concerns of COSATU's rank and file mirror those of the unemployed and the otherwise socially excluded. At the same time, those members who feel such concerns are also those who more frequently engage in strike action. In turn, this implies that unions are likely to be at the forefront of any new round of challenges to the status quo. However, the apparent durability of the present dominant partyism means that such challenges are likely to again take the form of struggles within the ANC Alliance, rather than through the development of an alternative political movement.