A fight over minimum pay for National Disability Insurance Scheme workers is under way at the workplace umpire, as unions claim some are being underpaid by $9 an hour.
The Australian Services Union, Australian Workers Union, Health Services Union and United Workers Union want providers to stop classifying staff as home care workers instead of social and community services employees.
The difference can be up to $9 per hour and it's estimated as many as one-in-10 providers underpay their staff, the unions say.
The case kicked off at the Fair Work Commission in Melbourne on Tuesday as they push for changes to the the Social, Community, Home Care and Disability Services Industry Award.
The award was written before the NDIS existed, and the union's application before the commission says the guidelines have ambiguity or uncertainty.
The unions are pushing for all workers in the scheme to get the higher pay rate, and the case does not involve the NDIS itself as its rates are covered under industrial law.
"We can no longer sustain a 'whack-a-mole' approach to deal with dodgy providers in the NDIS," Australian Services Union spokesman Angus McFarland said.
"There are too many rorts and workers being ripped off.
"We are taking action in the Fair Work Commission to ban this practice once and for all."
He stressed the case is not about pushing for wage increases or extra funding but instead ensuring workers are paid minimum award rates.
The federal government is attempting to pass a suite of NDIS reforms aimed at reining in costs, which would reduce the number of eligible new participants and change funding criteria.
The annual cost of the NDIS is expected to surpass $50 billion by 2025/26, which is higher than the annual cost of Medicare.
NDIS Minister Bill Shorten said the case was about ensuring people were in the correct category for work they were actually doing, and it was "entirely unexceptional" for unions to take it to the commission.
"Unions have raised the issue that some people working in the sector are being underpaid, or misclassified when they should be being paid more at a higher category, the independent umpire will have a look at that issue and work through the issues," Mr Shorten told reporters on Tuesday.
