Plaid Cymru has pulled out of a cooperation agreement with Welsh Labour, attacking the new first minister, Vaughan Gething, in a lengthy statement.
Plaid Cymru leader Rhun ap Iorwerth said that while he is "proud of the way in which the agreement demonstrated a new way of doing politics", he does not have confidence in the judgement of the first minister.
He said: "I remain deeply concerned that the first minister has failed to pay back the £200,000 donation to his leadership campaign from a company convicted of environmental offences, and believe it demonstrates a significant lack of judgement."
Mr Gething has defended his decision to take the donation, and has refused to return it, despite pressure from Plaid Cymru and the Welsh Conservatives.
He added that he is "worried by the circumstances around the decision to sack" Hannah Blythyn as minister for social partnership yesterday, whom Mr Gething accused of leaking to the media (which she denies).
The agreement was a joint policy programme between the two parties that covered 46 areas of governance - ranging from education, social care, housing, and tourism.
It was due to end in December of this year anyway, and is not hugely surprising ahead of a Westminster election expected this year.
But it puts pressure on Mr Gething, who has served as first minister for less than two months.