Live Register figures for last month have shown the biggest increase in more than six years.
The Central Statistics Office said the seasonally adjusted figure rose to 169,700, the highest figure for three and a half years.
This represented an increase of 5,000 compared with October, the biggest rise since November 2001. The Live Register has been on an upward trend this year, and a note from Davy Stockbrokers said today's figures strongly suggest that builders are losing their jobs, as the increase in males signing on was significantly higher.
A separate CSO measure of employment in the construction sector, also published this morning, showed a 4.9% fall in October compared with the same month last year.
The unemployment rate was 4.6%, up from 4.5% in October. The CSO said there were monthly increases in all regions, with the largest in the Mid-West and the smallest in Dublin.
The Live Register is not regarded as a measure of unemployment, as it also includes part-time workers and seasonal workers entitled to benefits or allowances.
