The Construction, Forestry, Mining and Energy Union says Thiess and Xstrata are exaggerating a downturn in commodity prices in order to justify sacking workers in north Queensland.
ABC News reports CFMEU spokesperson Steve Pierce said a decision to sack 95 mining workers at Collinsville was unnecessary and motivated by greed.
"They're saying that the market is shot, the industry is dead," he said.
"Well, they are still making in excess of $100 a tonne for coal that three or four years ago were getting $40 and $50 a tonne for, so they are still making damn good profits.
"We need to dispel the myths that is being perpetrated by the coal industry that they are going broke."
Pierce said while the mining industry was keen to cut workers at early signs of volatility, it could also be caught “whinging and moaning” about the lack of skilled labour.
Last month Theiss and Xstrata said they would attempt to redeploy some of the workers impacted by the job cuts, and the move was unavoidable because of a downturn in the coal market.
Late last year the CFMEU also criticised Vale and its joint-venture partner Sumitomo for axing workers from the Isaac Plains mine in central Queensland.
But while most coal operations continue to downsize and lay off workers, approval for Gujarat NRE's $20 million longwall 5 expansion at the Russell Vale project is set to allow for the continuation of 500 coal jobs.