The Register writes visits to the United States may soon require you to share details about your Facebook and Twitter account. Under a new proposal by the US Customs and Border Protection (CBP) agency, an optional field would be added to the I-94 travel form and the Electronic System for Travel Authorization (ESTA) visa application, asking you to share "information associated with your online presence/social media identifier." At least for now, it would be an optional field to be used for vetting purposes.
"Collecting social media data will enhance the existing investigative process and provide DHS [Department of Homeland Security] greater clarity and visibility to possible nefarious activity and connections by providing an additional tool set which analysts and investigators may use to better analyze and investigate the case."
The CBP already does some social media monitoring of incoming travelers, as was shown in 2012 when two visitors were detained on arrival and held for questioning, before being deported 12 hours later, because of comments one of them had made on Twitter.