The Construction Forestry and Mining Union (CFMEU) says it is concerned construction companies are taking money from government subsidies but not paying Indigenous trainees.
Darwin’s $34 billion liquefied natural gas (LNG) project provides a significant boost to the Northern Territory economy.
The LNG webpage shows that nearly 80 per cent of sub-contractors are local firms.
But one of the most influential unions in the country says fair treatment of Indigenous workers on the site is in question.
"We think it's a great opportunity to get into the construction industry, but the training needs to be real, job opportunities need to be real, and we shouldn't see Indigenous employment used as a way to milk money out of government subsidies by big construction companies," says Dave Noonan from the CFMEU.
The CFMEU says they are concerned that Aboriginal trainees on the INPEX project are not happy.
"It appears they were compelled to do six weeks training without payment. There are concerns raised that a number of them have undertaken or been given certificates of competency for operating heavy plant equipment they weren't properly trained on," said Mr Noonan.
The federal government is investigating these allegations.