Four tech firms are suing Facebook Inc. in the US because of its anticompetitive behavior, and are demanding that the Chief Executive Officer Mark Zuckerberg give up his control in the social network.

In a federal lawsuit filed on Thursday in San Francisco, the four firms— Cir.cl, Beehive Biometric, Reveal Chat and Lenddo, accused the tech giant of running “the most brazen, willful anticompetitive scheme in a generation” in the 2010s.

The quartet also said that if Zuckerberg is not forced to sell his majority of shares in Facebook, it will integrate them into a giant social network, “consolidating its market power across the globe, likely permanently foreclosing competition in the relevant markets for decades to come.”

The tech firms described Facebook as “one of the largest unlawful monopolies ever seen in the United States”.

The lawsuit builds on the increasingly loud argument that major internet platforms are required to undergo greater scrutiny for their power to swallow up small businesses in their vicinity.

Facebook is currently facing multiple regulatory probes.

The big internet platforms are facing a high level of scrutiny of their business practices after years of virtual inaction in Washington. Both the Justice Department and the Federal Trade Commission, which share a mandate to enforce antitrust laws, have announced broad reviews of the technology sector – indicating that Facebook and possibly Amazon.com Inc. will undergo parallel investigations by both agencies.

Meanwhile, a Bloomberg report quoted Facebook as saying, “We operate in a competitive environment where people and advertisers have many choices,” adding, “In the current environment, where plaintiffs’ attorneys see financial opportunities, claims like this aren’t unexpected but they are without merit.”

(With input from agencies)