This article brings the neglected topic of small professional unions into the women and unions literature. In addition to an overview of women’s representation and gender equality strategies in small professional UK unions, it offers a contextually grounded analysis of barriers and enablers of women’s participation in Napo – the union representing professional workers in the probation service. The article identifies several enablers: healthy levels of women’s representation over a long period of time; presence and longevity of gender equality strategies; a strong occupational identity; occupational values that complement those of unionism. However, a highly pressured work environment and hostile industrial relations climate create lived insecurities, work–life imbalance and time poverty, which have constrained women professionals’ union participation.