They're going to need a very big room for the hearing if the scope is expanding to include all user profile/activity data-centric advertising-based apps/services
"It’s the third such request that lawmakers have made of Facebook Chief Executive Mark Zuckerberg to testify since it emerged earlier this month that Cambridge Analytica, a data firm hired by President Trump during the 2016 campaign, may have improperly accessed names, “likes” and other personal information from at least 30 million Facebook users.
But the Senate Judiciary Committee’s hearing spells the first time that congressional lawmakers have expanded their scrutiny to include Zuckerberg’s peers, Google CEO Sundar Pichai and Twitter CEO Jack Dorsey. The result could be a hearing that exposes both of those tech giants – whose data is not known to have been taken by Cambridge Analytica – to uncomfortable questions about the extent to which they profit from their users’ most personal data, too."Congress wants to drag Google and Twitter into Facebook’s privacy crisis - The Washington Post