Any attempt to sell off Channel 4 would require a change in the law that would be fought "tooth and nail", according to an SNP MP.
John Nicolson, MP for East Dunbartonshire, called on opposition parties to unite to oppose any move to privatise the broadcaster.
David Cameron has said that the UK Government will "look at all of the options" for the future of the channel, including private investment.
He had been asked by Mr Nicolson, the SNP's spokesman on culture, media and sport, to confirm that there were no plans to sell Channel 4 during Prime Minister's Questions.
Mr Nicolson said a new House of Commons library paper confirmed that "privatisation would require legislation addressing the statutory framework that currently underpins Channel 4 and its obligations".
He said: "We all know that this Government's majority is wafer thin and the SNP will use its numbers to try and defeat any attempt to privatise Channel 4.
"Today I'm calling on others from across the chamber to join us in standing against this assault on the broadcaster.
"The Tory plans for Channel 4 risk the valued output of what is an essential public service broadcaster.
"That is why the SNP will fight tooth and nail against any moves towards privatisation, including by opposing the full primary legislation that would be required before any such privatisation could happen."
A spokeswoman for the Department for Culture, Media and Sport said: "The Government has made no decisions regarding reform of Channel 4.
"Channel 4 has an important remit and we are looking at a range of options as to how to continue to deliver this, including options put forward by Channel 4."