Secretary of State Julian Smith reminded MLAs their salaries cost more than £15m while Stormont was out of action
Finance Minister Conor Murphy has said a proposed extra £1 billion in funding from Westminster for the Stormont Executive is "woefully inadequate".
The Government said on Wednesday evening they will add an extra £1 billion in funding to the new Stormont Executive bringing tjeir total support to £2 billion.
Mr Murphy said public services will now face a shortfall of at least £1 billion next year, making them "extremely difficult" to fund.
He accused the Government of acting in bad faith, saying they undertook to provide the additional funding needed to deliver "ambitious" commitments in the New Decade, New Approach deal.
Meanwhile, Secretary of State Julian Smith said politicians' salaries had cost £15m while Stormont was out of action - and said "let's get on with it".
"Let’s remember MLAs have been off work 3 years at a cost of £15m+ in salaries.," he said on Twitter.
"There will be a new deal for NI as it leaves the EU. There is also a UK budget in spring. £2bn is biggest ever NI talks settlement & it addresses a number of key issues."
Finance minister Murphy said his officials were in the process of fully costing what was required but that the announcement had been made against the wishes of the First Minister and Deputy First Minister.
Mr Murphy said: "The financial package claims to provide £2bn. £1bn of this was already coming to the Executive."
In a statement on Wednesday, the Government said they were providing the funding to end the nurses’ pay dispute, transform public services, turbocharge infrastructure investment and address NI’s unique circumstances.
They said it included a "rapid injection" of £550 million to Executive finances, including £200 million to resolve the nurses' pay dispute and deliver pay parity over the next two years, as well as £60 million for a medical school in Londonderry and £50 million for public transport.
Mr Murphy said: "For the legacy institutions, the proposed package adds £100m to the £150m previously committed. This falls at least £50m short of the projected cost of £300-£400m.
"The parties are working together to deliver quality public services for our people. This act of bad faith makes our job much more difficult.
"As Finance Minister I cannot and will not accept this and will be taking this up with the British Government."
Julian Smith, Secretary of State for Northern Ireland, said: "New Decade, New Approach is about putting Northern Ireland’s Assembly on a sustainable footing.
"This funding provides certainty to the Executive and ensures much-needed reforms across health, education and justice can be delivered."
Earlier on Wednesday, Conor Murphy visited the Casement Park sports ground in West Belfast which is awaiting a long-delayed overhaul.
Parts of Northern Ireland's infrastructure and wider public services have suffered during the three-year devolution hiatus.
Final resolution of an unprecedented nurses strike which has paralysed parts of the health service was also earlier awaiting confirmation of new funding from the UK Government.
The deal which sealed the return of the Northern Ireland Executive includes an intention to complete planned stadia programmes.
The construction of a new stadium at Casement Park was badly delayed by safety concerns and objections from residents.
A renewed business case came into Stormont's Communities Department in November.
It is intended to be a centrepiece for Gaelic Athletic Association (GAA) games in Northern Ireland.
The project has an overspend of £33 million, a recent Audit Office report said.
Building has still not started three years after the expected completion date.
SDLP leader and MP Colum Eastwood said he will be raising the matter of the "totally deficient" financial package in Westminster.
"The gulf between the ambition of the deal and the money on the table is substantial and will cause serious public finance difficulties for the Executive. This is not, and cannot be, the end of the matter.
"I am, however, pleased to see earmarked and ring fenced allocations for the expansion of Magee and a new addiction centre for the North West. These were priorities that I raised with the Secretary of State on behalf of the people of Derry. I intend to see both critical projects delivered for our city.
"I will be raising this matter at Westminster as a matter of urgency."