Mark Drakeford has been accused of abusing his position as First Minister in the run up to the Senedd Election by Plaid Cymru.
Party leader Adam Price has written to the Permanent Secretary of the Welsh Government, Dame Shan Morgan, who is the charge of the civil service.
In the letter, Mr Price accuses the First Minister of using civil service resources for electioneering purposes, which must not be done during an election period.
Adam Price highlights an interview on the BBC last night where Mark Drakeford said he will use Friday's Welsh Government briefing to set out what a Labour government, if successful, would do in the three weeks following the election.
By doing so, Mr Price says the First Minister has broken the pre-election guidance which states 'Welsh Government communications activity must not be seen or perceived to be influencing, or potentially influencing the outcome of the election on behalf of any political party...'
Lifting of Covid restrictions ahead of schedule, and without input from opposition parties, has also been cited by Mr Price in his letter.
He claims this is in breach of the agreement to provide advance notice to all parties of any changes.
"It goes against the spirit and letter of our understanding with the Welsh Government during the pre-dissolution period."
The Plaid Cymru leader also accuses the First Minister of misleading the public when he claimed in last night's BBC interview that the Welsh Government had "no support from opposition parties" in tightening restrictions before Christmas.
Mr Price writes: "This is categorically untrue, evidenced by the fact that the BBC reported on December 15th that Plaid Cymru had been pressing the case for tighter restrictions.
"At a time of heightened political awareness, I seek your guidance on how I can best ensure that the First Minster corrects this inaccuracy."
Mr Price has called on the Permanent Secretary to arrange an urgent meeting ahead of Friday to discuss fairness in the election campaign and to "review the arrangements in place for sharing factual information - including scientific modelling - on a fair and equal basis to all prospective First Ministers."
The Permanent Secretary has not yet responded to the Plaid Cymru letter.
The Welsh Conservatives have also commented after Mark Drakeford's interview on the BBC and called for the Chief Medical Officer, Dr Frank Atherton, to lead Friday's coronavirus press conference instead of the First Minister.
Janet Finch-Saunders, member of Welsh Conservatives, has called it "questionable" that changes to Covid-19 restrictions have been made during the election period.
"Welsh Conservatives believe pandemic-related announcements could and should be fronted by senior civil servants such as the chief medical officer, and this should be the case on Friday.
"Sadly, last night's comment demonstrates these announcements are nothing other than naked electioneering by Labour, and it's sad to see the First Minister once again using people's livelihoods as pawns in his political games."
A Welsh Labour spokesperson said: “Mark Drakeford remains the First Minister making important decisions to keep Wales safe.
“We are aware that Mr Price has sent another letter, we understand this will be responded to in due course.”