The UK faces a "democratic crisis" with voters being targeted with "pernicious views" and data being manipulated, a parliamentary committee is set to warn.
The Digital, Culture, Media and Sport (DCMS) Committee has been investigating disinformation and fake news following the Cambridge Analytica data scandal.
In its first report, MPs will suggest social media companies should face tougher regulation or a new tax.
It also proposes measures to combat election interference.
The MPs' report comes after months of investigating the impact of technology giants and how people are affected by the rise in fake news on social media.
It also probed whether Russia had a role in influencing voters in the EU referendum.
The committee's report was due to be officially published on Sunday.
But a copy was leaked on Friday by Dominic Cummings, the director of the official Brexit campaign group Vote Leave, who published it on his own blog.
Mr Cummings was asked and officially summoned to take part in the inquiry – to respond to allegations made against the Vote Leave campaign – but he refused. Mr Cummings called the report "fake news".
According to the leaked report, MPs say "our democracy is at risk and now is the time to act".
The committee highlights the "relentless targeting of hyper-partisan views, which play to the fears and prejudices of people, in order to influence their voting plans".
The report is expected to be very critical of Facebook, which has been under increased scrutiny following the Cambridge Analytica data scandal.
"Facebook has hampered our efforts to get information about their company throughout this inquiry. It is as if it thinks that the problem will go away if it does not share information about the problem, and reacts only when it is pressed," it will say.
"It provided witnesses who have been unwilling or unable to give full answers to the committee's questions."
It will repeat its call for Facebook chief Mark Zuckerberg to give evidence.
The committee's report will also say it had received "disturbing evidence" – some of which it had not published – of hacking, disinformation and voter suppression in elections since 2010.
"We urge the government to ensure that the National Crime Agency thoroughly investigates these allegations."
BBC
