Derbyshire County Council must cut an extra £5million because of Tory spending over the last three months, it has been claimed.
Councillor Anne Western, leader of the Labour group at the authority, said the Conservative administration now needed to make savings of £85m - up from £80m - by 2022.
But Coun Barry Lewis, leader of the county council, stressed the authority was 'well on track' to making the £85m cuts - and insisted bosses had identified £18m in reserves which 'more than covers that £5m'.
Coun Western said: "Since taking control in May, they (the Conservatives) have spent money on manifesto commitments without identifying where the cash is coming from, hence the cuts total has increased from £80m to £85m."
But Coun Lewis responded: "Along with authorities across the country, we need to make savings - £85m across five years in Derbyshire to be exact.
"On the face of it, these are daunting numbers - but we immediately set about assessing every penny the county council spends and carrying out forensic examination of money held in its reserves.
"I'm pleased to say we're well on track to make those savings.
"In addition, we've already identified around £18m which can be released from reserves, in line with our priorities, with the expectation that we'll find more. This more than covers that £5m Coun Western refers to.
"While a detailed examination of reserves is important in helping to manage our finances in the short-term, it will not deflect from us making appropriate long-term budget savings and day-by-day we're finding ways of delivering services more efficiently and effectively."
On his 100th day in office, Coun Lewis said the county council had, among other things, already axed parking charges at Matlock Bath, scrapped costs for taking rubbish to its recycling centres and pledged an extra £6m for fixing potholes and repairing roads.
He also said the authority was 'on course' to freezing council tax for two years from 2020 and would save more than £300,000-a-year by controversially cutting its top management team, including the post of chief executive.
Coun Lewis added: "I make no apology for having the courage to think differently to get the results which benefit the county's residents.
"But we have to be realists and acknowledge that there'll never be enough money or staff to provide all the public services everyone wants to see in an ideal world - we're not living in utopia.
"Of course, some decisions will not be universally liked.
"At times they will be controversial and will attract headlines - we'd expect that.
"If you do things in the same way you get the same results and we can't do that.
"We're making bold decisions to do things differently and we welcome public scrutiny.
"It's been a busy first 100 days.
"It would have been easy to postpone making the difficult decisions - but that's not what this authority is about.
"We recognise the challenges we face and are prepared to meet them head on."