NUM has accused Glencore of failing to comply with its social and labour plans in regards to the severance packages.
The mining union has asked the South Africa Department of Mineral Resources (DMR) to "enforce compliance".
The mining company previously said that it would go ahead with its plans to close some of its Optimum Coal operations due to weak coal prices.
Optimum produces around 10 million tonnes of coal annually; out of which half is exported and half of it sold to power utility Eskom.
The mine is expected to be placed on care and maintenance, and a large part of the operations is likely to be reopened if market conditions improve.
Reuters cited NUM Deputy General Secretary William Mabapa as saying: "We are consulting with our lawyers as to what recourse we will take against DMR if they fail and Glencore succeeds with retrenchment."
Glencore however dismissed these charges from the mining union.
Glencore was cited by news agency saying: "We have continually engaged with all parties … in order to determine whether measures were available to avoid the closure.
"It was demonstrated during these sessions that these operations are financially not viable in the current market conditions and that there are no measures available to avoid the retrenchments."
