Deputies and other staff members at Wongawilli will be hit hard by Wollongong Coal's decision to place the mine in care and maintenance mode, their unions say.
The deputies and supervisory staff from the mine met on Thursday afternoon to be briefed on the impact of the decision and, while final numbers were not available, the union said about 90 per cent of employees were being made redundant.
"Today's announcement is a hard day for our members and their families," Collieries Staff and Officials Association director Catherine Bolger said.
"Our members have been loyal workers for the company over the last 18 months, even at times when they weren't paid regularly.
"These workers have done everything in their power to ensure the survival of the mine.
"It is extremely regrettable that the company has placed the mine on a 'care and maintenance' footing," Ms Bolger said.
"Our members are very disappointed and sad that it has come to this.
"This announcement comes at a very difficult time in the coalmining industry, so this will have a massive impact on these staff."