The Australian Manufacturing Workers Union says the LNG giant, Woodside, has a moral obligation to its local workforce as a number of people face losing their jobs at the Karratha Gas Plant.
The union says up to 70 Transfield employees are facing unemployment as the result of a recent change in contractors, despite many working on site for more than ten years.
Monadelphous has signed a $150 million contract with Woodside to conduct maintenance work at the plant from early next year.
The union's WA president Tony Hall says it appears Monadelphous will now bring in its own workforce for the project.
"The commitment we had from Monadelphous is 'yeah, yeah, we will pick up a good portion of the current employees' so everyone was happy with that response," he said.
"None of the current employees have actually been picked up.
"There should be a moral obligation upon a contractor and upon Woodside as well, to actually pick up people that live in this town." Mr Hall says it calls into question Woodside's commitment to the local community.
"These are people that have lived and worked in Karratha for up to ten years or more," he said.
"Their families are here, their kids are here, their lives are here.
Not one of these people, who've got the required skills to do the work at that gas plant, have been picked up at this stage." In a statement to the ABC, Woodside did not confirm or deny the sackings.
It says it remains committed to its workforce in Karratha.
However, a company spokeswoman says the number of employees required on site fluctuates as projects start and finish.
Monadelphous has been contacted for comment.