Nine social-media platforms and video-streaming services are being investigated by the Federal Trade Commission in the US, the agency announced.
Amazon, YouTube, Facebook and WhatsApp are among the largest tech companies involved in the investigation.
"Social media and video-streaming services have become almost unavoidable in today’s modern world, particularly as many Americans are working, socialising and attending school online during the national pandemic," said a statement from three commissioners who voted in favour of the investigation.
The order also included Discord, Reddit, Snap, TikTok owner ByteDance and Twitter.
The commission voted 4-1, with one abstention, to begin the investigation.
"Despite their central role in our daily lives, the decisions that prominent online platforms make regarding consumers and consumer data remain shrouded in secrecy," the statement said.
The commissioners say their aim is to have a greater public understanding of how social-media platforms and video-streaming services collect, store and use consumer data.
The order also requested information on how user data fits into business plans, and the agency specifically asked how the companies handle child and teen user data.
The decision comes alongside a growing conversation around Big Tech and how companies balance obtaining and using data with maintaining privacy.
As extensive technology use has grown during the pandemic, user privacy and security are being more highly scrutinised.
"Critical questions about business models, algorithms and data collection and use have gone unanswered," said commissioners who voted in favour of the investigation.
"It is alarming that we still know so little about companies that know so much about us."