Miners at Kellingley colliery have been sent redundancy notices as UK Coal bosses press ahead with plans to close the troubled pit.
The letters have been sent to 57 workers at the colliery, where around 700 could eventually lose their jobs.
The pit near Knottingley and Thorseby Colliery in Nottinghamshire are both under threat after the company ran into financial problems.
UK Coal said the pits would both shut by the end of 2015 under a “managed closure plan”.
But the National Union of Mineworkers is looking at plans for an employee buyout which could save hundreds of jobs.
Pontefract and Castleford MP Yvette Cooper said: “This is very bad news. UK coal should not be making redundancies while work is underway on serious plans to try to keep the pit open.
“It’s really grim for the mine workers and their families who are getting redundancy letters now, and it’s really worrying for the rest of the workforce too.”
Bosses at UK Coal, which has been hit by cheaper coal imports from abroad, said the managed closure plan must go ahead to prevent the pit’s immediate closure.
But they are helping the NUM with its bid to launch a buyout which would see the mine run by its workforce.