The lobby group Greypower fears a nine-day working fortnight may have a negative effect on superannuation payments.
The scheme, devised at the job summit in February, provides a government subsidy to those who agree to drop a day's work each fortnight.
An adjustment in superannuation payments is due on 1 April and will be based on the cost of living and the average wage.
Greypower says if the nine-day fortnight reduces the average wage, it will also force down superannuation.
However, the Government says any impact its job support scheme could have on superannuation would be minimal. It estimates that in the absence of other changes to wage levels, the nine-day fortnight could lead to the average wage being lowered by about 0.1%.
Job support scheme
The job support package is available to employers with more than 100 employees. Ten employees will be eligible for every redundancy averted.
Those who agree to work one day less a fortnight will get the adult minimum hourly wage of $12.50 from the Government - but for only five hours a fortnight.
The Government estimates that about 1,600 companies fall into that category, and expects up to 25,000 employees will take it up, at a cost of about $20 million.