On the basis of matched employer–employee data from 2007 to 2009, this paper examines the union wage gap among small and medium non-state manufacturing enterprises in Vietnam. Controlling for both worker and firm characteristics, the results provide evidence that union members earn higher wages than non-members, and are more likely to receive social benefits.Within unionised firms, a substantial wage premium is revealed for workers employed in Southern firms, a finding which among other factors may be attributed to historical differences between the North and South of Vietnam.