First Minister Rhodri Morgan is facing demands to explain why he blocked a Welsh barrister's appointment to the assembly's highest legal post.
Gerard Elias was recommended by an independent panel
BBC Wales' Dragons Eye programme has learned that Gerard Elias QC was recommended for the £140,000-a-year job of counsel general by an independent panel.
It has been claimed that Mr Morgan vetoed the recommendation because he wanted another barrister with strong Labour connections.
But Mr Morgan's office described opposition claims that Labour "cronyism" was at the heart of the decision as "absurd".
The leaders of the Conservatives and of Plaid Cymru in the assembly, Nick Bourne and Ieuan Wyn Jones, both said it raised very serious issues about whether the proper rules had been followed.
They are both demanding a statement from the first minister.
The Welsh Assembly Government and the Civil Service Commission - which oversees the recruitment process - both said the procedure was fair.
Mr Morgan wanted another QC, Malcolm Bishop, who has stood as a Labour candidate and is a close associate of former Lord Chancellor Derry Irvine.
But Mr Morgan's office said the first minister did not know, had never met and had never spoken to Mr Bishop.
Mr Elias is one of Wales' most eminent barristers. He was recommended for the post of counsel general - the assembly's chief adviser on legal matters - by an independent interview panel.
The post became vacant following the retirement of Winston Roddick QC.
Malcolm Bishop was First Minister Rhodri Morgan's choice
But senior assembly and legal sources have told Dragon's Eye that Mr Morgan opposed his appointment because Mr Elias was a freemason and had a connection to hunting, in that he was an adviser to a pro-foxhunters' body.
Mr Jones said the first minister had some "very serious" questions to answer.
"He has got to come clean with us," he said.
"If it is true and these acts of cronyism are there then he needs to satisfy us that he has acted even handedly.
"He has to make a statement so we can understand the role he took.
"Did he try and influence the panel in any way on the appointment of someone who has strong connections to the Labour party?
"And what were his reasons for turning down the appointment of the first person? We need to know."
Liberal Democrat AM Eleanor Burnham is also calling on Mr Morgan to explain his actions.
"It's important that we have independence as the job is very important to Wales and independence is vital to the job," she said.
No-one has been appointed, and the assembly government is considering what to do next.
One senior assembly source described the affair as a constitutional scandal of the highest order.
Glyn Davies, Conservative AM for Mid and West Wales, described the situation as "a constitutional outrage".
He said : "The counsel general is the highest paid person employed by the assembly and must be seen as truly independent of government to be effective.
Mr Davies said Mr Morgan's involvement "raised real questions" about whether the counsel general could serve the whole assembly.
"I have sought the advice of the previous counsel general on sensitive issues in the past and would not have done so if I thought there was a political link with the Labour government," he added.
Dragons' Eye is broadcast on BBC 2W at 2030 GMT on Thursday and on BBC 1 Wales at 2335.