Four high-profile British politicians have called for Rupert Murdoch's Twenty-First Century Fox to be blocked from buying Sky.
The four, including former Labour leader Ed Miliband, say the mogul will be able to influence its news output despite promises to the contrary.
Murdoch is locked in a battle with US cable giant Comcast to buy Europe's biggest pay-TV group, with the Australian-born tycoon hampered by his ownership of other assets in Britain including two leading national newspapers.
In order to gain regulatory approval Fox has offered to guarantee the independence of the Sky News operation by funding it for 10 years and creating a fully independent board to oversee it, a move that led analysts and competition lawyers to say the deal would likely be cleared.
But four lawmakers who have previously criticised Murdoch's influence in Britain said in a letter to the regulator that the offers did not go far enough.
They noted that the chief executive of Sky would still appoint the head of Sky News. "This is a significant statement because other statements made have tended to imply that the Editorial board will somehow be in charge of the process, not the Sky CEO," they said.
Fox agreed a deal to buy the 61% of Sky it did not already own in December 2016 but it has been repeatedly delayed by the government and regulators. It is likely to learn whether it can take over Sky in the middle of June.
Fox has said it does not agree with the regulator's objections but has offered to protect Sky News to help secure approval. Fox has agreed to sell a string of assets on to Walt Disney, including Sky.
Comcast has offered £12.50 per share or £22.1 billion for Sky compared with Fox's offer of £10.75 per share, but it has not yet made a formal bid and is trying to secure its own regulatory approval.
The four lawmakers are Miliband; Vince Cable, the leader of the Liberal Democrats; Conservative MP Ken Clarke, a and Charles Falconer, a former Labour justice minister.
"We would urge the panel to come to a clear finding in favour of prohibition, consistent with its powerful provisional findings," the letter said.