The Corrections Department is cutting the hours of community work supervisors in Canterbury but disagrees that the cuts are due to low offender turnout.
The National Union of Public Employees said its members' hours were being reduced because Corrections was not doing enough to force those sentenced to community work to turn up.
Figures released to RNZ News show that only 30 percent of offenders turned up for their community work in February and, in Canterbury, the figure was just 24 percent.
Union spokesperson Janice Gemmell said about 20 staff in Canterbury had been told their hours were being cut by 40 percent.
It was Corrections' job to ensure offenders carried out their sentences, Ms Gemmell said.
"They're just not putting the resource into the sentence... These aren't as high a risk as, say, your prison guys, the ones who are sentenced, who might be your murderers and your rapists," she said.
"These are considered to be slightly less risky - yet it's their job to ensure these offenders actually do comply with, and do, their sentence."
However, the Corrections Department said the cuts were not the result of low offender turnout - and, instead, pointed to the changing nature of sentences.
The main reason the department was cutting the hours of staff supervising those doing community work was that fewer people were being sentenced to do the work, it said.
It said a 40 percent drop in the number of people being sentenced to community work in the past five years meant the reduction in staff hours was the best use of its limited public resources.