Plans to create a broadcast archive for Wales have been thrown into doubt after the Welsh Government withdrew support.
The £9m project at the National Library of Wales (NLW) in Aberystwyth was due to become home to 160,000 recordings from the BBC Wales programme archive.
Culture minister Lord Elis-Thomas has told the library he cannot commit £1m to the plans in their current form.
The move has been called "outrageous" by opposition politicians and NLW said it was "disappointed".
But the Welsh Government said the plan may put the library at long-term risk.
Plaid Cymru AM Dr Dai Lloyd said Wales faced the "loss and destruction of an irreplaceable archive" and said Lord Elis-Thomas's actions were "completely unacceptable".
Dr Lloyd added: "He is foregoing his responsibilities as a minister and putting the entire project at risk."
BBC Wales has said it is "disappointed" the project will not go ahead in its planned form, as it would have seen extensive broadcasting history "gifted to the National Library of Wales for everyone to explore and enjoy".
What is the National Broadcast Archive?
While largely comprising of BBC Wales programmes, the new archive was also expected to contain material from S4C and ITV Wales.
The project would allow the BBC Wales archive to be preserved when the broadcaster leaves its headquarters in Cardiff, while the public would be able to access the material digitally at special viewing centres in Aberystwyth, Cardiff, Carmarthen and Wrexham.
There would also be regular events and activities related to the archive at the National Library in Aberystwyth and the three viewing centres.
Lottery funding of £5m has been agreed in principle, but a final application to the Heritage Lottery Fund is yet to be submitted by the National Library.
In a letter to library president Rhodri Glyn Thomas seen by BBC Wales, culture minister Lord Elis-Thomas said he wanted to make clear his dissatisfaction ahead of a meeting of the Library's trustees on Friday, who are due to make a final decision on the plans.
He said: "Based on the project plan and its financial estimates, I remain unwilling to commit either the £1m capital funding that has been requested or to provide strategic support for the National Broadcast Archive in its current form."
Lord Elis-Thomas notes that he had previously requested a review and a thorough redesign of the project, but this had not taken pace. He added that steps needed to be taken "to ensure the National Broadcast Archive does not endanger the financial stability of the National Library in future".
While Lord Elis-Thomas said he accepted some discussions about the project's long-term sustainability had since taken place between the National Library, BBC Wales and other interested parties, he remained "disappointed" that the work had happened "so late in the process".
The letter said information previously provided by the library "makes clear that some of the library's existing activities are likely to be negatively impacted" by the project.
A Welsh Government spokesman added: "Whilst we have expressed support in principle for the ambition of the National Library of Wales to establish a National Broadcast Archive for Wales, the Welsh Government will not be supporting the project in its current form.
"We have concerns that it could potentially risk the financial stability of the National Library in the long-term."
The library's president Mr Thomas, said they were "very disappointed".
He added: "The library's board of trustees will discuss the minister's decision at its meeting on Friday before making any further comment."