The Federal Trade Commission sued to break up Facebook on Wednesday, asking a federal court to force the sell-off of assets such as Instagram and WhatsApp as independent businesses.

“Facebook has maintained its monopoly position by buying up companies that present competitive threats and by imposing restrictive policies that unjustifiably hinder actual or potential rivals that Facebook does not or cannot acquire,” the commission said in the lawsuit filed in federal court in Washington, D.C.

The lawsuit asks the court to order the “divestiture of assets, divestiture or reconstruction of businesses (including, but not limited to, Instagram and/or WhatsApp),” as well as other possible relief the court might want to add.

The announcement is a major step that has been years in the making, with Facebook and several other major U.S. technology companies having grown quickly in the past 10 years with little government oversight.

But the lack of scrutiny has changed recently, with a series of lawsuits that now threaten to rein in the dominance of big American tech firms that have grown to be among the world’s most valuable companies.

Attorneys general from 48 states and territories said they were filing their own lawsuit against Facebook, reflecting the broad and bipartisan concern about how much power Facebook and its CEO, Mark Zuckerberg, have accumulated on the internet.

Facebook’s share price fell by as much as 4 percent after the news, before paring its losses.

“Breakup Facebook” has become a rally cry for the company’s critics — from Sen. Elizabeth Warren, D-Mass., to one of Facebook’s wealthy founders, Chris Hughes, who last year wrote a 6,000-word case for a break-up. But the idea has never been truly attempted in court.

Facebook said it was reviewing the two lawsuits, and pointed out that the FTC approved the Instagram and WhatsApp acquisitions at the time.

“Years after the FTC cleared our acquisitions, the government now wants a do-over with no regard for the impact that precedent would have on the broader business community or the people who choose our products every day,” Facebook said in a statement, adding that it would have more to say soon.

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