Social media companies have been warned they face "severe" fines if they restrict free speech through their enforcement of online safety laws.
Platforms including Facebook, X, Instagram and TikTok have been told by ministers they must not limit access to posts which express lawfully held views.
It presents a shift in tone from the Government after a backlash to the Online Safety Act.
According to campaigners, the Government's application of the Online Safety Act, which is supposed to protect children from harmful content, is a threat to free speech.
Now, Whitehall sources are said to have expressed concern that some social media firms "have been overzealous" in their enforcement of the law, and said the companies must be "mindful" of the right to freedom of expression.
The Science Department, which oversees the legislation, told firms they risk facing fines if they do not uphold free speech.
A spokesman said: "As well as legal duties to keep children safe, the very same law places clear and unequivocal duties on platforms to protect freedom of expression.
PA
|Platforms including Facebook, X, Instagram and TikTok have been told they must not limit access to posts which express lawfully held views
"Failure to meet either obligation can lead to severe penalties, including fines of up to 10 per cent of global revenue or £18million, whichever is greater.
"The Act is not designed to censor political debate and does not require platforms to age gate any content other than those which present the most serious risks to children such as pornography or suicide and self-harm content.
"Platforms have had several months to prepare for this law.
"It is a disservice to their users to hide behind deadlines as an excuse for failing to properly implement it."
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The Government has received a backlash against the Online Safety Act
However, others have criticised Labour's threat, and said it is only in response to US pressure.
Earlier this week US Vice President JD Vance warned the West had become "too comfortable with censoring" in a meeting with David Lammy.
His comments to the Foreign Secretary are the latest in a string from the US regarding the state of free speech in the UK.
Last week, the Trump administration said it is "greatly concerned" after a secretive Whitehall "spy" unit was revealed which targeted social media posts criticising migrant hotels.
HOUSE OF COMMONS
|Julia Lopez, the shadow Science Secretary, has criticised the Government's actions regarding the Online Safety Act
Discussing Labour's warnings, Lord Young of Acton, the founder of the Free Speech Union, said: "This feels performative to me. An attempt to reassure JD Vance that the British Government takes free speech seriously.
"In reality, the free speech duties under the Act are a joke and the chances of Ofcom fining a social media firm for failing to comply with them are vanishing to zero."
Meanwhile Julia Lopez, the shadow Science Secretary, said: "The Government must to everything to ensure the Act doesn't become a blunt tool to block people's freedom.
"But given their approach and attitude towards free speech so far, it's hard to believe they will do the right thing."
Rebecca Vincent, the interim director of Big Brother Watch, said: "Online censorship is rapidly on the rise and we're now in a ludicrous situation where all UK internet users only have access to a childproofed version of the web unless we're willing to undergo intrusive age verification processes.
"Unfortunately JD Vance is right when he says free speech in Britain is in retreat."