The £1 billion agreement between the Conservatives and DUP to prop up Theresa May's government led to immediate demands for similar boosts to devolved administrations in Scotland and Wales.
Welsh First Minister Carwyn Jones said the cash injection amounted to a "bung" which flew in the face of government commitments to fair funding for the nations and regions.
And Plaid Cymru said that Wales should receive around £1.7 billion to match the largesse provided by the government to Northern Ireland as part of the pact between the Conservatives and DUP.
The Welsh government put the figure at £1.67 billion over the course of the Parliament.
Mr Jones said: "Today's deal represents a straight bung to keep a weak prime minister and a faltering government in office.
"Only last week, we were told that the priority was to 'build a more united country, strengthening the social, economic and cultural bonds between England, Northern Ireland, Scotland and Wales'. This deal flies in the face of that commitment and further weakens the UK, and as currently drafted all but kills the idea of fair funding for the nations and regions.
"It is outrageous that the prime minister believes she can secure her own political future by throwing money at Northern Ireland whilst completely ignoring the rest of the UK. I have spoken to the secretary of state for Wales this morning to clearly state my view at this unacceptable deal - as Wales' voice at the Cabinet table, he has a duty to fight against this deal and secure additional funding for our country."
Plaid Cymru's leader in Westminster, Liz Saville Roberts, said: "Despite Wales voting overwhelmingly to reject the Conservatives, we seem destined to be governed by the Conservatives once again, propped up by an extreme right-wing party opposed to gay rights, who criminalise women who have an abortion and is supported by armed terror groups.
"Our country did not vote for this government and Plaid Cymru will oppose this government at every step of the way.
"Any commitments for Northern Ireland should be matched for Wales. If reports that the DUP has secured a £1 billion increase in public spending in Northern Ireland are realised, Wales' population share would be around £1.7 billion - a substantial boost to the Welsh economy that must be delivered."
Meanwhile, the agreement was denounced as a "shoddy little deal" by Liberal Democrat leader Tim Farron, who accused Mrs May of throwing taxpayers' money around to preserve her own position.
Mr Farron said: "The public will not be DUPed by this shoddy little deal. The nasty party is back, propped up by the DUP.
"While our schools are crumbling and our NHS is in crisis, Theresa May chooses to throw cash at 10 MPs in a grubby attempt to keep her Cabinet squatting in Number 10.
"It would be better for the people of Northern Ireland for the DUP to buckle down and focus on the talks process to restore devolved Executive at Stormont, to bring the political stability that is needed for inward investment and growth, rather than demanding cash injections from the Treasury."
Green Party leader Steven Agnew said: “This is a deal dominated by tax breaks for big business and so is a missed opportunity to put people first by prioritising public service spending.
“Any money allocated to health and education could be undone by the reduction in corporation tax, which would cost around £200 million.
“Our schools and hospitals are under great pressure - Westminster deals will matter little if the Stormont stalemate isn’t resolved.”
Adam Marshall, director general of the British Chambers of Commerce, said: "Since the General Election, the top priority for business communities across the UK has been a workable government that can do more than just tackle Brexit negotiations.
"Action is needed now to improve the environment for business and industry here at home. For business, action on the economy will be the true test of the success of the Conservative-DUP deal over the coming months."
UK Scottish Secretary David Mundell has previously said he "won't support funding which is deliberately sought to subvert the Barnett rules".
He said: "We have clear rules about funding of different parts of the United Kingdom. If the funding falls within Barnett consequentials, it should come to Scotland."
