The US federal regulators and more than 45 state prosecutors have sued Facebook, accusing the social media company of taking illegal actions to buy up rivals and stifle competition.
The lawsuits are one of the most significant legal actions the US government has taken against the firm.
Officials are asking the court to consider breaking up the company, which also owns Instagram and WhatsApp.
Facebook said the deals under scrutiny were approved by regulators years ago.
“The government now wants a do-over, sending a chilling warning to American business that no sale is ever final,” Facebook general counsel Jennifer Newstead said.
She said the company had invested millions to make Instagram and WhatsApp successful and would defend itself “vigorously”.
“Antitrust laws exist to protect consumers and promote innovation, not to punish successful businesses,” Facebook said, describing the government’s arguments as “revisionist history”.