America's Federal Trade Commission has resumed work today, including its probe into Facebook, and is being urged by advocacy groups to hand the organisation a $2bn fine and break up the social networking empire.

The FTC launched its investigation after last year's Cambridge Analytica scandal led to various admissions about the scale of data shared with developers and other companies.

The work had been put on ice during the US government's 35-day shutdown – the longest in its history – though the agency is back in the saddle as of today after funding was temporarily reauthorized.

In a letter (PDF) to the agency, nine groups, including the Electronic Privacy Information Center and the Government Accountability Project, said Facebook had "operated for too long with too little democratic accountability".

The group said it was remarkable that the FTC hadn't imposed a single fine against Facebook since it handed down its consent decree in 2011, despite what the group said were "repeated violations".

"Based on the duration of the violations, the scope of the violations, and the number of users impacted by the violations, we would expect that the fine in this case would be at least two orders of magnitude greater than any previous fine," the letter said.

"We anticipate that the fine against Facebook would exceed $2 billion," it continued, based on the $22m the FTC fined Google for the Safari hack.

The letter – published before it was revealed that Facebook was planning to integrate Messenger, Instagram and WhatsApp – said the Social Network™ had breached its commitments "regarding the protection of WhatsApp data" and should be required to "unwind the acquisition" of the platforms.

"The companies should be reestablished as independent entities and Facebook should be required to disgorge the personal data unlawfully acquired from those firms. This will also help restore competition and innovation for Internet messaging and photo app services, two important goals for the future of the Internet economy."

The signatories also called for the firm to work harder to hire a more diverse leadership, and even went so far as asking the FTC to recommend to Congress that Facebook be regulated as a public utility. ®