LABOUR is demanding an inquiry after Kirklees Council underspent by £9.6m.
Angry party leaders said they would have urged a council tax decrease if the figures had been known earlier.
Labour group leader Clr Mehboob Khan said: "The ruling Lib Dems wanted a council tax rise this year twice the size of Labour proposals, yet we now find they were not able to spend the money they already had.
"The Lib Dems had predicted a modest overspend of £330,000 but when the final accounts were done the figure was wrong by a massive £10m.
"Labour councillors will be asking for a full and open inquiry into this latest blunder."
Lib Dems hit back - saying the surplus was good news and meant there would be cash reserves available for services.
Council leader Clr Kath Pinnock said: "It shows there are good financial controls in place and that we have been prudent about spending.
"It's good news because it means we have some resources to set aside for calls on it.
"Personally, I would rather be in this position than that of other councils faced with cutting services."
She said the underspend amounted to less than 2% of the council's £410m budget.
Clr Pinnock said: "It is not unusual and there were underspendings of this order under previous Labour administrations.
"I'm disappointed that Clr Khan is so out of line with previous Labour leaders."