The four main party leaders in Wales have taken the unusual step of writing jointly to the Prime Minister calling for an independent review of S4C.
Carwyn Jones, Ieuan Wyn Jones, Nick Bourne and Kirsty Williams said "political stewardship of S4C has been insufficiently vigilant."
The Department of Culture, Media and Sport (DCMS) has said funding S4C will pass almost entirely to the BBC.
The Wales Office said the UK government was committed to an independent S4C.
In the letter obtained by BBC Wales the leaders of Welsh Labour, Plaid Cymru, the Welsh Conservatives and Welsh Liberal Democrats say they want the review to be comprehensive.
They also say they believe that the term of office of the current S4C Authority, which has been blamed for much of the recent problems, should end after the review has been completed with a new governance structure.
They said the review should ensure that S4C remains independent as a Welsh publisher-broadcaster.
In a joint statement First Minister Carwyn Jones and Deputy First Minister Ieuan Wyn Jones underlined the value of S4C.
"It is of incalculable importance to the further strengthening of the Welsh language as well as to the successes of Wales' creative industries sector," said the statement, "and it has an important role to play in ensuring much-needed plurality within Wales' media.
"We have laid out a constructive plan with the intention of ensuring a secure and independent future for S4C. We now await the Prime Minister's response."
Downing Street confirmed that the letter arrived, and that the Prime Minister's office would respond in due course.
BBC correspondents said it was "extremely significant" that the leaders of the Welsh Tories and Lib Dems had joined the leaders of Welsh Labour and Plaid in writing to Mr Cameron.
But a Wales Office spokesman said: "The government is committed to the future of Welsh language programming and to the future of S4C as an independent entity.
"We believe the best way to ensure S4C offers the best possible service to its audience while also securing its future is through a new funding arrangement involving the BBC.
"The Wales Office will continue to work with S4C and the DCMS to ensure the interests of Welsh language broadcasting are taken fully into account."
Nick Bourne, leader of the Welsh Conservatives, said it was important that there was a cross-party approach on the Welsh language and on S4C in particular.
Speaking on BBC Radio Wales Mr Bourne denied that his involvement in the letter showed a lack of influence with his party colleagues at Westminster.
"It's not that at all," he said.
"The importance of the letter is to stress the fact that this is a united view in Wales and I think there's goodwill on all sides. I think there's goodwill at Westminster as well.
"There's a period of time when we can sort this out and I'm appealing for that to happen. I think the response, that it is being taken seriously, is the appropriate response and I hope we can all move forward together."
S4C said it had nothing to say about the letter as it was a matter for politicians.
Meanwhile, Welsh Office Minister David Jones has met members of Cymdeithas yr Iaith Gymraeg (the Welsh Language Society) to discuss the future of the channel.
The society is is calling for people to refuse to pay the TV licence fee unless the independence of S4C is guaranteed.
Mr Jones said during the meeting he sought to address some of the society's concerns, highlighting that the new arrangement will secure the future of the channel.