Nottinghamshire's Thoresby colliery will close by the end of next year at the latest, as part of a phased scaling-down of mines by UK Coal.
The company - the UK's largest coal producer - currently employs 2,000 people across the country, including around 600 at Thoresby.
It is currently in talks for an emergency cash injection of between £10 million and £20 million from the government and the private sector to continue operating until the end of 2015.
It comes after competition from cheap imported coal put pressure on business.
A spokesman for the firm said cutbacks would be made even if the emergency cash is secured.
We have started today consultations with the unions on looking at the way forward - that is, looking at reducing numbers in the coming months.
We are looking to secure the best outcome possible.
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Further showers or longer spells of rain for many tonight, heavy at times, particularly over the hills.
Further blustery showers are likely through the night, with these heaviest and most numerous towards the west.