270 jobs could be affected after the owner of Aberpergwm Colliery in the Neath Valley begins talks on whether to suspend activity.
American firm Walter Energy says the proposal is a "result of a challenging economic environment which continues to heavily impact the global coal industry".
The firm insists that during the consultation period most of the employees will remain at home on full pay.
However up to 100 employees may be required to continue working at the mine to continue development works within the upper drift.
Early indications are that if the firm proceeds with the outlined proposals only a small number of employees would be retained to keep the mine in a safe condition until operationsresume.
More top news
Showers in the north will spread southeastwards overnight. Temperatures will be higher so not as chilly as list night.
Chilly start to Tuesday, turning into a largely fine and dry day.
Political Editor Adrian Masters was joined in the studio by assembly members Bethan Jenkins, Mick Antoniw and Suzy Davies.