More than 150,000 public service workers are in line for a reduction in their working week from July.
It's after review by an Independent Body has recommended extra unpaid hours introduced in 2013 are reversed.
The government will consider the proposal, which would benefit the likes of nurses, education and local authority staff, this week.
SIPTU Deputy General Secretary, John King, says the extra hours that were introduced negatively impacted workers' morale.
"It was a counter productive measure in that it served to demotivate."
He believes reducing the work week will give a "overall boost" to the public service.
The report is before Government this week.