GLENCORE has denied reports that employees at its Oaky North mine near Middlemount were told to return to work or risk losing their jobs.
Last week mining union CMFEU said workers were given an ultimatum after raising concerns about black lung.
"At no point were workers threatened with job loss," said a Glencore spokesman.
"At some point on Thursday we had discussions with the workforce... as of 5pm they returned to work."
CMFEU district president Stephen Smyth said the workers were reluctant to go underground on Thursday following reports of three Queensland coal mine workers contracting black lung.
The potentially-fatal disease is caused by dust inhalation and can develop into lung cancer.
Mr Smyth said he did not believe Glencore's denial.
"They've put the fear of god into workers who had genuine safety concerns," he said.
A Glencore spokesman said the company would check all employee's x-rays upon request.
"The health and safety of our workforce has always been our top priority and we appreciate the concerns raised by employees about this issue," he said.
Yet Mr Smyth said he wasn't convinced B readers would be used to read the x-rays comprehensively.
"They'll tell you that the people are trained to an Australian and New Zealand standard but are they trained to a standard to read the x-rays to ensure they're clear of dust or black lung?" he said.
"We say they're not, based on the information we've got from the mines department and other people."
Mr Smyth said all Queensland coal mines were offering checks of concerned workers' x-rays.
None of the reported cases of black lung have involved Glencore's underground operations.
Black lung - reported cases:
- Two workers from Carborough Downs mine, near Moranbah.
- Percy Varrall, a former Ipswich coalfields worker.
- CMFEU say there may be hundreds more cases.
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