DUP MLA Gordon Lyons was speaking after SDLP MPs called for Dublin to have a consultative role in NI’s budget while the NI Assembly is suspended.
The party's two MPs, Claire Hanna and leader Colum Eastwood, have tabled an amendment to the Budget Bill which would mandate the UK Government to engage with the Irish Government on NI’s budget.
Secretary of State Chris Heaton-Harris NI Budget Bill will be debated by MPs after summer recess. The Assembly remains dormant because the DUP is seeking reforms of the Windsor Framework.
Mr Eastwood said: “For 19 months people have been waiting for the DUP to get back to work."
He added: “The DUP can’t be allowed to call the shots anymore. They need to understand that power-sharing will endure whether they like it or not and whether they take part or not.
“In the absence of an Executive, the spirit of the agreement must be facilitated by enhanced co-operation between the British and Irish governments.”
Ms Hanna added: “We need a new approach, new thinking to create solutions to these problems and it would be prudent to approach some of these on an all-island basis.”
However the DUP said the idea runs counter to the Belfast/Good Friday Agreement (GFA).
“In making this call the SDLP are actively seeking to step outside the Belfast Agreement," Gordon Lyons said. "If that is the case then they should have the honesty to say so. Northern Ireland’s budget is a matter for the United Kingdom Government and the local parties alone.
“Whilst it is dressed up with talk of ‘new thinking’... their only solution to any situation is to put forward some cross-border proposal.”
He said the DUP is the only party pointing out that the UK Barnett Formula is “not fit for purpose” in relation to public spending in NI.
“Instead of all-Ireland fantasy politics, the SDLP should focus on securing practical and workable solutions which recognise the political environment in which we exist.”