The US government and 48 attorneys general have filed landmark anti-trust lawsuits against Facebook, seeking to break up the social networking giant over charges that it engaged in illegal, anti-competitive tactics to buy, bully and "kill" its rivals.
Twin lawsuits filed in the federal district court allege Facebook under its chief executive Mark Zuckerberg behaved for years as an unlawful monopoly.
It was claimed it had repeatedly "weaponised" its vast stores of data, seemingly limitless wealth and savvy corporate muscle to fend off threats and maintain its stature as one of the most widely-used social networking services in the world.
The state and federal complaints chiefly challenge Face- book's acquisition of two companies - Instagram, the photo-sharing tool, and messaging service WhatsApp.
Investigators said the purchases ultimately helped Facebook remove potentially potent rivals from the digital marketplace, allowing the tech giant to enrich itself on advertising dollars at the cost of users, who as a result have fewer social networking options at their disposal.
The lawsuits together represent the most significant political and legal threats to the company in its 16-year history, setting up a high-profile clash between US regulators and one of Silicon Valley's most profitable firms, which could take years to resolve.
Anti-trust regulators explicitly asked a court to consider forcing Facebook to sell off Instagram and WhatsApp to remedy their competition concerns.
Such a punishment would unwind Zuckerberg's digital empire and severely constrain Facebook's ambitions.
The Federal Trade Commission (FTC), led by Republican chairman Joe Simons, brought its lawsuit in a District of Columbia district court.
Letitia James, the Democratic attorney general of New York, led her Democratic and Republican counterparts from dozens of states and territories in filing their complaint in the same venue.
The lawsuits drew a swift response from Facebook, which pledged to "vigorously defend" its business practices.
"People and small businesses don't choose to use Facebook's free services and advertising because they have to, they use them because our apps and services deliver the most value," said Jennifer Newstead, the company's vice-president and general counsel.