Conservative leaders are demanding action on what they call the growing threat of online censorship from social media giants, including Facebook, Twitter, Google and YouTube.
The letter to Attorney General William Barr has been signed by over 30 people, including Brent Bozell, President of the Media Research Center, Brian S Brown, President of the National Organization for Marriage, William A Donohue, President of the Catholic League, LifeSiteNews editor John-Henry Westen, and Tim Wildmon, President of the American Family Association.
They say that concerns over online censorship should be a 'high priority' for his office and that there is an 'urgent' need for the Department of Justice to investigate Facebook, Twitter, Google and YouTube.
They go on to claim that the social media platforms pose 'existential threats to the conservative movement and indeed American society as a whole'.
'At this point, it is undeniable that Facebook, Twitter, and Google/YouTube all have a significant liberal agenda hardwired into their platforms,' the letter reads.
'These platforms also have an unprecedented power to manipulate and sway elections. Such sweeping power, combined with near monopolistic dominance in the marketplace, and in conjunction with deep one-sided liberal partisan bias within all these organizations, is cause for alarm.
'These organizations present a threat not merely to conservatives in the United States, but indeed our free market economic system and the very viability of the U.S. political system.
'Respecting these entities' own constitutional rights, we believe there nevertheless is ample probable cause of antitrust violations and of conspiracy to violate the constitutional rights of conservatives, and possible collusion to violate laws governing America's campaign finance system and elections.'
The letter cites occasions where conservative perspectives have been blocked on the social media sites.
These include reports of adverts promoting pro-life movie Roe v Wade, starring Jon Voight, being blocked by Facebook, and an apology issued by the social media company to evangelical pastor Franklin Graham after he was banned for 24 hours over a 2016 post that was critical of relaxing bathroom policies for transgender people.
Elsewhere, concerns were raised over a recent interview by Twitter CEO Jack Dorsey in which he admitted neutrality was not a goal.
'I don't believe that we can afford to take a neutral stance anymore. I don't believe that we should optimize for neutrality,' he said.
The conservative leaders also questioned a $250,000 donation from Google's charity arm to the Southern Poverty Law Center, which has branded several Christian organisations as 'hate groups', including the Alliance Defending Freedom, which defended Christian baker Jack Phillips after he was sued for refusing to make a gay wedding cake.
The letter concluded: 'Americans are distrustful of these social media organizations because they have good reason to be. Their institutional bias against conservatives, along with their massive influence, makes for a dangerous combination and one which can deliberately tilt the outcome of elections.
'During such a turbulent time in our nation's political system, it is crucial that you investigate how these social media/search media powerhouses wield their power to sway elections.'