The Construction, Forestry, Mining and Energy Union (CFMEU) says it is concerned about recent cuts to permanent staff numbers at mines in Queensland's Bowen Basin.
The CFMEU says Anglo Coal has cut permanent jobs at two of its central Queensland operations.
There is also speculation permanent positions will also be cut from the Collinsville mine, north-east of Mackay, which is operated by Thiess.
A Thiess spokesman says while staff numbers are being reviewed at Collinsville, there are no current plans to cut staff numbers beyond natural attrition.
CFMEU spokesman Steve Smyth says it has been more than a decade since permanent staff were targeted as part of cost-cutting measures.
"In the late 1990s, early 2000s, we had some lay-offs," he said.
"In the GFC [global financial crisis], it was again labour-hire and contract workers that were laid off but permanent workers you'll have to go back to late 1990s and early 2000s.
"That's one of the things about mining being in cycles.
"We've had a lot of people come in when mining's been good and all of a sudden we're in a bit of a slowdown and they go, they all start worrying, but that is mining." He says the industry needs to better managed.
"We expect the employer, when times do slow down, they should look after their employees, not just throw them on the scrap heap like they have been," he said.
"It's outrageous and our concern is now they'll just start running the line through those sorts of guys and ladies and we'll end up in a position where we have less people in permanent roles.
"The companies will want that flexibility of bringing in contractors and labour hire that they can just do what they like with them."