First Minister Vaughan Gething has come under more pressure after Plaid Cymru ended its co-operation deal with Labour in Wales immediately.
Plaid leader Rhun ap Iorwerth said he was proud of what the deal achieved but said he was "deeply concerned" about £200,000 given to Mr Gething's leadership campaign by a company owned by a man twice convicted of environmental offences.
The deal saw Plaid help the Labour-run Welsh government - which has exactly half the seats in the Welsh Parliament - get through important votes .
It comes during a turbulent week in the Senedd for Mr Gething after he sacked one of his ministers.
Conservatives have mooted tabling a no-confidence motion, to try to force his resignation.
Labour Members of the Senedd (MSs) met to discuss Plaid pulling out of the deal on Friday evening.
A member of Mr Gething's cabinet, Mick Antoniw, said after the meeting the Labour group was united behind the first minister.
In the wake of the meeting, Mr Antoniw said there was "complete unity" behind the first minister.
"We are confident everyone will stand behind the first minister in a no-confidence vote," the counsel general told BBC Wales.
Mr Gething said he was “disappointed Plaid Cymru has decided to walk away from their opportunity to deliver for the people of Wales”.
What is the co-operation agreement?
The meeting was called to talk about the end of the Plaid deal, but whether Mr Gething's leadership was discussed has not been made public.
The three-year deal between the two parties was agreed in December 2021 under Mr Gething's predecessor Mark Drakeford, after the Senedd election where Labour secured 30 seats - one short of an outright majority.
It was not a formal coalition, but meant Labour and Plaid worked together on 46 policy areas.
Crucially, the deal meant that Plaid supported Welsh Labour ministers in getting their budget through the Senedd.
It also meant in practice that Plaid had an incentive to keep the Welsh government functioning, having a direct interest in its agenda.
The ending of the deal potentially frees Plaid to support a no-confidence motion, if one was tabled, without facing questions over its involvement in the deal.
It also means Labour will have to make ad hoc deals with opposition parties on votes and legislation in future - although that was due to be the case at some point anyway as the deal was due to end by the end of the year.
Speaking to BBC Radio Wales Drive, Mr ap Iorwerth said there was a “lack of judgement around receiving that money, the way it happened, and refusing to pay it back”.
He was referring to Mr Gething’s £200,000 campaign donation from Dauson Evironmental Group, and said it was a central motivating factor in pulling out of the agreement.
“I think people of the Labour party and elected members agree that this did not feel right, that there is a clear perception of a conflict of interest. He should have paid it back,” he said.
He added that “a change in attitude by the Welsh government towards the agreed programme” of the co-operation deal, for example planned changes to council tax which were postponed earlier this week, also contributed to the decision.
“The first minister himself has been asked to carefully consider his actions in the past few months. He has decided he is going nowhere and is fighting to clear his name.”
Asked if he would support a no-confidence vote, he added: “This one’s for Labour.”
He added that the "offer still remains to continue to work together", but said "our relationship will be different from now on".
It emerged during Mr Gething's Welsh Labour leadership campaign that he had received the £200,00 donation.
He narrowly beat Jeremy Miles - now his economy minister - to the Welsh Labour leadership on 16 March, and formally became first minister on 20 March.
On Thursday, he sacked his minister for social partnership, Hannah Blythyn, alleging that she leaked text messages to the media.
It followed a story, originally published by Nation.Cymru, which revealed Mr Gething told ministers he was deleting messages from a pandemic-era group chat.
Mr Gething has since announced that Ms Blythyn will be replaced by Bridgend MS Sarah Murphy.
Mr ap Iorwerth said he was “proud” of the co-operation agreement's achievements in policy areas such as free school meals, free childcare, housing, energy and the Welsh language.
But he said he was "worried" by the circ*mstances around the decision to sack a member of the government this week relating to matters that should be in the public domain already.
In response, Mr Gething described the co-operation agreement as "mature politics".
“While it was always a time limited agreement, we are disappointed Plaid Cymru has decided to walk away from their opportunity to deliver for the people of Wales,” he said.
He added the Welsh government would look at how it could still progress commitments attached to the agreement, including on Welsh language education and fair housing.
Analysis - David Deans, political reporter
This is deeply unhelpful for a government that, since Vaughan Gething became first minister in March, has been under fire week after week.
The agreement was likely to end soon anyway - Plaid has strongly suggested it would end earlier than original expiration date of December.
But the timing is crucial. Ending it at this moment is more politically damaging to the first minister as he faces the potential of a vote of no-confidence in the Senedd.
It frees up Rhun ap Iorwerth to go on the attack, without having to worry about complicated relations with the governing party.
The end of the deal means that Labour will perhaps need to find another way to get its next budget through the Senedd – maybe through Welsh Liberal Democrat leader Jane Dodds - although in reality it was going to need to do that anyway.
The news on Friday is more about the drama that Plaid is ratcheting up, and the pressure it puts on Vaughan Gething.
