The Service and Food Workers Union is pushing for home support workers to be paid for the time they spend travelling between clients.
It has filed a case with the Employment Relations Authority, asking it to send it to the Employment Court.
National secretary John Ryall believes it is illegal for organisations' home support workers not to be paid at least the minimum wage for the time they spend travelling between clients.
He says while many are employed currently for an eight hour day, when travel time is taken out, some get as little as six hours' pay.
Mr Ryall says cleaners and security guards are paid as they move around, so home support workers should be paid on the same basis.