Israeli journalists have appealed to a British billionaire not to proceed with the sale of a stake in an Israeli television channel, which they warn would represent a severe blow to the independence of the country’s media.

Sir Leonard Blavatnik, listed by the Sunday Times as the UK’s third richest person, is selling a nearly 15% share in Channel 13, a commercial channel that has run critical news coverage of Benjamin Netanyahu’s government in recent years, including investigations into the prime minister’s financial dealings.

Blavatnik is selling to a telecoms tycoon, Patrick Drahi, who has French, Portuguese and Israeli nationalities. Drahi already owns a cable television company and a news channel in Israel that generally runs far less critical coverage of Netanyahu.

The rest of Drahi’s business empire is heavily in debt and he is embroiled in a legal battle with his creditors in the US.

The Union of Journalists in Israel issued a statement calling the sale an “unlawful deal, which is likely to further erode press freedom in the country” and described it as part of the Netanyahu government’s “master plan to capture the media” before this year’s scheduled elections.

“The Union of Journalists is confident that Sir Blavatnik, who is known for his generous philanthropy, will not support any move that will undermine press freedom in Israel,” the statement said.

Blavatnik is selling just under a 15% stake in Channel 13, the maximum share allowed to be sold to a competitor with an existing media asset under Israel’s competition laws, but critics argue that as the sole investor in the channel (Blavatnik is reportedly unwilling to invest further after years of heavy losses), Drahi will have real control of the outlet.

“While Patrick Drahi is only buying 15%, our fear is that by buying 15%, he gets 100% hold of the policy of the channel,” said Anat Saragusti, who oversees freedom of the press for the Union of Journalists. “Because if he’s the only one that can pour money into the channel and make it sustainable, then it is completely dependent on him.”

“It’s a lose-lose for the Israeli public, in terms of freedom of speech and diversity of opinions,” Saragusti added.

Drahi’s company, Altice, Netanyahu’s office and Israel’s ministry of communications were all approached for comment but did not respond.

Ayala Panievsky, a presidential fellow in journalism at City St George’s, University of London, compared the struggle over Channel 13 to the fate of the Washington Post under the US billionaire Jeff Bezos, who steered it closer to Donald Trump and last week axed nearly a third of its workforce, firing hundreds of journalists.

Panievsky last year published a book, The New Censorship: How the War on the Media is Taking Us Down, on the siege on the free press mounted by the populist right around the world. She views the Washington Post and Channel 13 cases as “part of the escalating war on independent and critical journalism, launched by the alliance of populist authoritarians and the broligarchy’s enablers”.

She said: “Media owners should be facing heat because they are in influential positions and are collaborating with governments to harm press freedom.”

Israeli journalists fear a Drahi takeover would lead to similar mass job losses as those suffered by their Washington Post colleagues.

A consortium of liberal Israeli tech entrepreneurs had made a rival bid for 74% of Channel 13. A source close to the group said it was prepared to invest considerably more – $80m to $120m (£59m to £88m) over three years – in the modernisation of the channel than Drahi and had put the offer on paper, though the negotiations had not been finalised.

A spokesperson for Blavatnik’s main company, Access Industries, denied there had been any political pressure to sell to Drahi. “Any suggestion that the preferred offer has been selected for political reasons is entirely false,” the spokesperson said. “Following negotiations with two separate groups, Patrick Drahi’s proposal was selected because it represented the better deal for [Channel] 13.”

The spokesperson added: “His offer enables the urgent injection of funds into the channel to support [Channel] 13’s stability, expand its reach, and allow its investment in high-quality content, innovation, and digital transformation, so it can continue delivering value to its audiences. Of the two proposals, it was the higher confirmed sum, and ultimately the stronger, faster option prevailed.”

The company denied Israeli reports that the Netanyahu government had signalled to Blavatnik that a purchase of the channel by the liberal tech consortium would not gain official approval. “Sir Leonard Blavatnik, nor anyone on behalf of Access, has spoken with any government official regarding [Channel] 13,” the spokesperson said.

Netanyahu and his ministers have mounted a concerted campaign to reshape Israel’s media landscape before this year’s elections. One set of corruption charges the prime minister is now on trial for involves the alleged offer of favourable financial treatment in return for positive coverage.

Last month a government minister sued an investigative journalist on the only other major independent news channel, Channel 12, for record damages of 12m shekels (£2.86m).

The government has imposed financial sanctions on the independent newspaper Haaretz, which it accuses of “support for the enemy” over its criticism of the Gaza war.

The tech consortium is expected to continue to argue its case for buying Channel 13, and the Union of Journalists said it expected Israel’s antitrust authorities or its supreme court to block the Drahi bid. Meanwhile, the reporters are hoping Blavatnik changes his mind.

“If Channel 13 falls, this would be the end of the free press in Israel, because the rest will fall after that. It’s the tipping point,” Saragusti said. “I think Blavatnik doesn’t really understand that this is not merely an economic issue but a milestone in Israeli democracy.”