Workers at doomed Kellingley Colliery claim delays are adding at least £1m per week to the cost of a deal that would keep the pit open until 2018.
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.
“Every week that goes by the government and UK Coal are hammering another nail into the coffin of the coal industry.
“As a rule of thumb every week that goes by is adding around £1m to the cost because that’s what it costs to run Kellingley.”
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 said: “The workers at the pit are really down and there’s a sense of inevitability about the place.
“There’s a lot of despair about it and the workers still haven’t accepted this bitter pill that we have got to swallow.”
Pontefract and Castleford Express MP Yvette Cooper said the delays were “disastrous” to the union’s plans.
Ms Cooper said: “People are already losing their jobs and if ministers don’t get a move on to get state aid soon it will be too late. With every week that goes by, it is getting more and more expensive to reopen the new development and save Kellingley from closure.
“Warm words from ministers about looking at European state aid are no good – we need action, fast.”
Ms Cooper called on the government to make a decision on the state aid deal by Christmas.
She added: “We simply cannot afford to wait any longer.”
No-one from UK Coal was available for comment when contacted by the Express.