The New Caledonian USTKE union says the government of the southern province will deploy an inspector to the Goro Nickel site to ensure Filipinos are only working in construction.
Goro Nickel is the largest industrial project in the South Pacific.
The company has hired some qualified Filipino workers who will help construct the two-billion US dollar plant.
But a union representative, Pierre Chauvat, says the Filipinos also work in other areas, such as in truck driving.
Mr Chauvat says the union met representatives from the southern province last Friday and says they have promised to look into the matter.
"We talked about the Filipino workers and the tasks that were given [to them] on the site at Goro. It appears that some of the Filipino workers are working in jobs they are not supposed to. There will be some heavy control on the site by the southern province on the administration of work."
The southern province could not be reached for comment.
A Goro Nickel spokesperson, Catherine Guillaume, confirmed earlier that some Filipinos worked in other areas than formerly agreed to because the company had difficulties finding locals for the job.