The Grosvenor mine has an employment model where the entire production workforce is supplied on a casual basis by labour hire company One Key.
The mine was the scene of ignition even earlier this year that led to five mine workers being hospitalised.
CFMEU Mining and Energy Stephen Smyth said all job cuts were a blow to workers and their families but casualisation and outsourcing made it easier for big companies to simply discard loyal workers when they were not wanted anymore.
"All of us in the industry have been shaken by the terrible events of 6 May at Grosvenor mine," he said.
"Workers at Grosvenor have had to deal with the trauma of those events, an ongoing inquiry into what occurred and uncertainty over the future of their jobs.
"Today they've had the terrible news that 100 positions will be cut."
Employment practices at Grosvenor have been in the spotlight at Queensland's Coal Mining Board of Inquiry, with Anglo CEO Tyler Mitchelson saying the outsourced, casualised model was the "safest" and "most productive".
The inquiry also heard evidence that contractors feared losing their jobs if they did not meet production targets.
Smyth said most of the mineworkers at Grosvenor had worked full-time at the site for years and were not genuine casuals.
"These are hard-working and loyal coal miners, but they have not been met with loyalty from Anglo in return through entitlements and job security," he said.
"Even if Anglo steps up and pays redundancy for One Key labour hire casuals in these unfortunate circumstances, it reinforces the question of why they were casuals to start with.
"There are very few genuinely casual jobs in coal production. These workers perform long shifts on long-term rosters. We need real change over employment practices in our industry."
A spokeswoman for Anglo American said since the suspension of longwall mining activities in May, the company has continued to support the Grosvenor workforce, to enable it to work through its future plans step by step.
Anglo American is also assessing opportunities to absorb some of the 100 impacted people into other roles at the mine, she said
"As part of planning work underway to support the safe restart of longwall operations in the second half of 2021, we have been reviewing our workforce plan to determine the best structure for Grosvenor going forward," she said.
"As an initial step, over the last month One Key Resources has been seeking expressions of interest from the Grosvenor workforce for voluntary redundancies," she said.
"Whilst there has been some interest in voluntary redundancies, there are discussions occurring with workforce representatives about how additional reductions can be achieved.
"Over and above what is required in workforce agreements, Anglo American will be providing redundancy benefits to the eligible One Key workforce impacted by the workforce reductions.
"After more than five months since we ceased production, we have reluctantly taken these steps to ensure that the mine can continue to support the majority of its remaining workforce, of around 650 people, and successfully return to safe production next year."