Department of Homeland Security (#DHS) stated asking travellers for their social media accounts (optional)
This does not apply to US citizens, but only visitors of 38 countries (mostly european) applying for the Visa Waiver programme via the Electronic System for Travel Authorisation (ESTA - ▻https://www.cbp.gov/travel/international-visitors/esta)
(▻https://travel.state.gov/content/visas/en/visit/visa-waiver-program.html)
▻http://www.politico.com/story/2016/12/foreign-travelers-social-media-232930
The U.S. government quietly began requesting that select foreign visitors provide their Facebook, Twitter and other social media accounts upon arriving in the country, a move designed to spot potential terrorist threats that drew months of opposition from tech giants and privacy hawks alike.
[...]
“The choice to hand over this information is technically voluntary,” he said. “But the process to enter the U.S. is confusing, and it’s likely that most visitors will fill out the card completely rather than risk additional questions from intimidating, uniformed officers — the same officers who will decide which of your jokes are funny and which ones make you a security risk.”
Opposition against this:
▻https://cdt.org/insight/coalition-letter-opposing-dhs-social-media-collection-proposal