New figures from the Central Statistis Office show that average annual earnings fell by 0.7% in 2013 to €35,830 from €36,079 the previous year.
The CSO said this compares with an increase of 0.5% between 2011 and 2012.
However, total annual earnings rose by 1.4% to €56.1 billion last year from €55.3 billion in 2012.
The CSO figures show that over the four years from 2009 to 2013, the information and communication sector saw the largest percentage rise over the period, increasing 14.7% from €58,594 to €67,208.
But the greatest decrease in average annual total labour cost over the four year period was seen in the construction sector which fell by almost 12% from €46,267 to €40,756.