Is it possible for trade unions to fight precarity in an adverse global context? Although existing research suggests this is possible, there is limited understanding of the interplay of resources that enable unions to address precarity in deregulated markets. This study employs a power resource approach to investigate how unions overcome their external constraints. It draws upon 130 in-depth interviews with key informants across nine Central and Eastern European countries to investigate successful and unsuccessful union actions in sectors with differing external resources. In each sector, unions that mobilise their internal resources have been able to reduce various precarity dimensions, such as low wages, lack of voice, and irregular working time. The results reveal that unions whose objectives are based on convincing win–win discourses can make strides, acting as drivers of change in precarity patterns even in unfavourable conditions. Moreover, the study introduces a multi-dimensional conceptualisation of union success, identifying union actions that result in measurable improvements in precarity dimensions for all worker types. To deepen understanding of the role unions play in fighting precarity in adverse contexts, future research could investigate union actions that improve a wider range of precarity dimensions for all workers.