Figures from the Central Statistics Office show a slight increase in trade union membership.
Read the full CSO report
The CSO said 34% of employees were union members in the second quarter of 2009 - up from 32% in the same survey a year earlier.
The results are taken from the CSO's Quarterly National Household Survey.
37% of full-time employees said they were members of a union, compared with 20% of part-time employees.
Among economic sectors the highest membership rate was in public administration and defence (81%) while the lowest rate was in accommodation and food service activities (6%).
