Four tech firms — two of which are now defunct — are suing Facebook on antitrust grounds and demanding that Mark Zuckerberg give up control of the company.

The four little-known firms banded together to accuse Facebook of running "the most brazen, willful anticompetitive scheme in a generation" in a federal lawsuit filed Thursday.

The four complained of Facebook's acquisition of WhatsApp and Instagram and said the firm's planned integration of the services would cement its dominance.

A Facebook representative told Business Insider: "We operate in a competitive environment where people and advertisers have many choices. In the current environment, where plaintiffs' attorneys see financial opportunities, claims like this aren't unexpected but they are without merit."

One of the lawyers representing the four complainant firms told Business Insider that Facebook "chose to use its might to intentionally eliminate its competition."

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Four tech firms are suing Facebook in the US on competition grounds and demanding that CEO and Chairman Mark Zuckerberg give up his control of the social network.

The four companies are Circl, an online marketplace and social network; Beehive Biometric, an identity-verification firm; Reveal Chat, a chat app; and Lenddo, a financial-services provider.

Two of the four — Circl and Beehive Biometric — are now defunct, while Reveal Chat was acquired by the music-streaming service Rhapsody in 2015.

In a federal lawsuit filed on Thursday in San Francisco, the quartet accused Facebook of running "the most brazen, willful anticompetitive scheme in a generation" throughout the 2010s.

They alleged that "the net effect of Facebook's anticompetitive scheme is one of the largest unlawful monopolies ever seen in the United States."

The lawsuit concluded by demanding that Zuckerberg "divest himself of incontestable control over the company."

Zuckerberg controls about 60% of Facebook's voting shares and acts as both CEO and chairman, giving him near-universal control.

The lawsuit refers to Facebook's ownership of the world's biggest social and messaging platforms, namely WhatsApp and Instagram. The four firms complained that Facebook's planned integration of these services "would increase the cost of switching to a rival social network" and might allow the surveillance of users.

"The integration, if completed, will not only substantially lessen competition, it may allow Facebook to destroy it — for a very long time," the lawsuit said.

The lawsuit builds on the increasingly loud argument that the big internet platforms deserve greater scrutiny of their ability to swallow up smaller competitors and to move into adjacent areas. Facebook is facing multiple regulatory investigations over antitrust allegations.

In July, the Federal Trade Commission launched a formal antitrust investigation into Facebook, while a bipartisan group of lawmakers on the House Judiciary Committee launched a similar probe in September.

The Justice Department also opened an official investigation into Facebook on antitrust grounds that month, as did a group of state attorneys general led by New York.

A Facebook representative told Business Insider: "We operate in a competitive environment where people and advertisers have many choices. In the current environment, where plaintiffs' attorneys see financial opportunities, claims like this aren't unexpected but they are without merit."

Meanwhile, Yavar Bathaee, a lawyer representing the four complainant firms, told Business Insider that Facebook had acted to deliberately crush its competition.

"Facebook faced an existential threat from mobile apps, and while it could have responded by competing on the merits, it instead chose to use its might to intentionally eliminate its competition," Bathaee said.

He continued: "Facebook deliberately leveraged its developer platform, an infrastructure of spyware and surveillance, and its economic power to destroy or acquire anyone that competed with them."

This story has been updated.