The Welsh Language Board has warned Rhodri Morgan that the language could suffer 'political mischief-making' under his planned reform of quangos.
The language body warned Morgan against abolishing the quango
The board fears it could become part of the Welsh Assembly Government in a shake-up to be revealed this month, and worries that this will affect its work.
The warning is in a letter seen by BBC Wales' Maniffesto programme.
Other quangos, including the Wales Tourist Board, have been told that they are to be part of his government.
In July this year, the first minister said that most Welsh quangos will be abolished within two years.
Quangos - which stands for quasi-autonomous non-governmental organisations - are semi-independent agencies of the assembly government.
They operate as arm's-length executive bodies responsible to boards appointed by ministers.
Mr Morgan said an announcement would be made this autumn on which organisations would come under the control of the assembly government.
He has already said the Welsh Development Agency, the Wales Tourist Board and the post-16 education body, Elwa, will cease to be by 2006.
The board's letter was written in the name of its chair, Meri Huws
However, Welsh Language Board members have written to Mr Morgan warning that any change to their organisation could damage the Welsh language.
The letter sent in late September in the name of board chair, Meri Huws, warns Mr Morgan that if he was to make the board part of the Welsh Assembly Government, it would be "irregular, untidy and give rise to conflicts of interest".
This, Ms Huws argues in that letter that is because of the difficulties the Welsh Assembly Government would have monitoring its own Welsh language schemes. Currently, the board does this.
The second objection, according to the board's chair, is the effect changing its status would have upon its current ability to make arm's-length decisions from the assembly government.
In the letter, Ms Huws warns that there is a danger "that incorporating the Board's duties within the Government would make the language less visible, giving the impression perhaps that the Government is cutting back on its support for the language".
The board also warn that there are "political advantages for the Government in having an arm's length body taking specific decisions within a strategic remit established by the Government directly".
Ms Huws adds in the letter, "It is certainly the case that decisions which are taken by specialist, impartial bodies are less likely to be the subject of political mischief-making than those taken by the Government directly".
No one from the Welsh Language Board was prepared to be interviewed about the content of the letter.
The Welsh Assembly Government said: "The Welsh Assembly Government asked the Welsh Language Board to respond to our considerations and we are grateful for their response, which is now under review."