Official figures show that average weekly pay in the first three months of this year was down 3.8% from the same period last year, with public sector earnings falling more sharply than those in the private sector.
Average weekly earnings were €682.91 in the first quarter, down from €709.55 a year earlier.
The CSO said this was due to a drop in average hourly pay and fall in the number of hours worked.
Weekly earnings in the private sector were down 2.8% from a year earlier, while earnings in the public sector dropped by 5.5%, as the effect of pay cuts introduced in last year's Budget took effect.
The CSO's figures do not take account of the public sector pension levy introduced in March last year.
Average pay fell in 11 of the 13 categories, with the biggest drop of 9.1% in the education sector. Transportation and storage pay fell 7.3%.
Average pay per hour in the private sector fell by 0.4% to €19.80, while in the public sector the drop was 3.7% to €28.87.
The CSO says average labour costs, which take other factors as well as pay into account, fell by 2.2% over the year to €25.46 an hour.
