Workers at doomed Kellingley Colliery claim delays mean a deal that would keep the pit open until 2018 would now cost at least £200m.
A £20m deal to carry out a ‘managed closure’ of the site between now and the end of next year was agreed in September.
But members of the National Union of Mineworkers (NUM) are trying to secure a state aid deal to keep the pit open for a further three years.
Keith Hartshorne, NUM delegate at Kellingley, said: “The state aid deal to save the pit until 2018 is a lot more expensive than it was because we’ve had no development.
“We’re not very hopeful that it will be agreed because the price of it is now looking like being at least £200m.”
Workers at the colliery have this week opened up another coal face – three weeks earlier than expected.
The NUM also claims the pit is now operating at a profit.
Mr Hartshorne said: “It’s just such a shame that all of our efforts won’t be allowed to continue.
“Even though we are running well into profit we are being prevented from doing that in the future.”
Mr Hartshorne said the state aid application was expected to be submitted this week.
But the ‘managed closure’ deal, which also includes funding from private investors, will see gradual job losses between now and the end of 2015.
Mr Hartshorne added: “It’s very hard to say what the mood is like down the pit.
“Personally I hate coming to work but it’s the only thing I know and that’s the worry if the pit closes – but everybody is still giving it their all.
“There’s a lot of anger and a sense of inevitability about the place but we just can’t understand why we can’t carry on when we are running at a profit.”
No-one from UK Coal was available for comment when contacted by the Express.