The Crown and two workers who were witnesses in the case will share the $45.9k penalty.
Mbie said this was the second such award made by the ERA against Osselton's businesses for her use of volunteers, with more than $20,000 paid to a Spanish worker employed by Karamea Holiday Homes.
A $5000 penalty was also paid in that case.
"Wherever a worker is being rewarded in a business at whatever level, the Labour Inspectorate's starting position is that these people are employees and minimum employment standards apply, including being paid at least the minimum wage for every hour worked," says Milne.
"Not only does exploitation take advantage of workers, it undermines businesses which do meet their obligations, and endangers the reputation of New Zealand as a fair place to live, work, and do business.
"Any other businesses making use of volunteer workers should take note of this case, and as both the Inspectorate and the ERA have made clear – workers have a fundamental right to be paid for all the work that they do."
Robinwood Farms is said to have exploited "thousands" of travellers through its volunteer scheme, according to Employment New Zealand.
The Labour Inspectorate's investigation found volunteers at the farm in Tai Tapu worked up to 40 hours per week cutting firewood and doing garden work, paid $120 per week in addition to food and accommodation.
Workers were not given employment agreements or paid minimum wage and annual leave entitlements.
A former worker described the living conditions of 'volunteers' at the property as 'inhumane', with many sleeping in a small storage room under the stairs without proper ventilation or a heater.
The Inspectorate was told volunteers were often supplied food collected from waste bins at supermarkets and spoiled meat.
