The broadcaster, which set up a national headquarters in Leeds in 2019, is owned by the Government and receives its funding from advertising, but could be sold off as a consultation on privatisation is due to be launched in the coming weeks.
The Labour mayor, who has previously worked as an actor, said the move has “rightly sparked much concern within the creative industry” and it could threaten Channel 4’s “commitment to diversity and inclusion”.
She also said the broadcaster has “brought vital investment” to West Yorkshire, but if it is sold off the region’s economy could suffer.
“The choice to relocate represents Channel 4’s commitment to Northern regions and towns and demonstrates a genuine belief by those in charge that our talent, knowledge, creative skill and technical ability can rival anywhere in the nation,” she said.
“These are values that are enshrined in the public service model of Channel 4, and privatisation risks the promises made by Channel 4 to make more programmes outside of London and the South East. So, I would ask the Government – what do you stand to gain from privatising?
“Channel 4 is made for us, at no cost to us, and the current model is working. We have a stake in the channel, and at present, the channel has a commitment to the things that matter to us.
“Privatisation risks losing the things that make Channel 4 so precious to us and risks stifling economic recovery and cultural revolution of places like West Yorkshire.
“We must not let this happen.”
Culture Secretary Oliver Dowden has previously said the consultation into privatising Channel 4 is aimed at ensuring the broadcaster “keeps its place at the heart of British broadcasting”.
But Channel 4’s chief executive Alex Mahon questioned the “logic” behind the decision and asked whether privatisation would support the Government's levelling up agenda.
“Would it deliver this public remit in the same way?” said Ms Mahon, during an interview with Times Radio.
“And particularly, would it be focused on how you level up outside of London, you know, now we’re spending 50 per cent of our money outside of London, big offices in Leeds, Manchester, Glasgow and Bristol.
“That’s a very, very different thing, perhaps to the motivation of a profit-based US streamer.”
She added: “Part of the reason that we’ve moved so many roles outside of London was because actually when I came in,
“I thought we’re not representing the UK properly. We don’t have opinions of people across the UK. And that’s a problem, right?
“You can’t be there as a public organisation to represent all over the UK and not be doing that.”
Earlier this week Channel 4 announced it recorded a record financial surplus of £74m in 2020.
It saw demand for All 4 streaming grow by 26 per cent, with more than 1.25bn views, and an 11 per cent increase in digital advertising revenues.
The broadcaster said there was also a three per cent increase in TV viewing in 2020 and a “strong recovery” in the advertising market after the initial impact of the Covid-19 pandemic.
Channel 4 expects its revenue to exceed £1bn in 2021 for the first time ever and said it is planning to invest an extra £40m in content over the next two years.