The closure of Tahmoor mine has been brought forward a year, to 2018.
The company has also called for expressions of interest in voluntary redundancies now, and a further call is expected early next year.
It is understood the company is looking for as many as 30 workers to take a redundancy.
In June owner Glenmore said the mine would close by early 2019.
“The decision has been made as a result of continued low prices in global coal markets, which has meant the economic return from reserves still available at Tahmoor are not sufficient to warrant the investment required to mine them,” a company spokesman said at the time.
However a decision on the future of mining Longwall 32 has brought forward the closure of the mine.
“The decision on Longwall 32 has been under review since the mine closure announcement was made,” a company spokesman said.
“It is now apparent, based on current economic conditions, that returns from Longwall 32 will not justify the additional investment required.”
That decision has prompted the move to offer voluntary redundancies.
“The decision at Tahmoor will mean some development work will cease immediately with voluntary redundancies being offered,” the Glencore spokesman said.
“All development work will be completed by early 2017, when further reductions in employees will take place.
“All mining is expected to end in early 2018.”
The company spokesman declined to respond to questions about whether forced redundancies were on the table.
However, there is the suggestion that could be an option if the voluntary redundancy process does not deliver enough applicants.
The workers have until mid-next week to put forward their expressions of interest.
The company spokesman said its coal portfolio was always under review.
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