Homeland Security Secretary John Kelly said the move could come as part of an effort to toughen the vetting of visitors to screen out people who may pose a security threat.
He said it was one of the steps being considered, especially for visitors from seven Muslim-majority countries with very weak background screening of their own such as Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen.
The seven countries were targeted in President Donald Trump’s controversial immigrant and refugee ban order which has since been suspended.
Mr Kelly told a hearing of the Homeland Security Committee: “We’re looking at some enhanced or some additional screening.
“We may want to get on their social media, with passwords.
“It’s very hard to truly vet these people in these countries, the seven countries. But if they come in, we want to say, what websites do they visit, and give us your passwords. So we can see what they do on the internet.”
He said anyone who refused to cooperate would not be allowed into the United States.
He stressed that no decision had been made, but tighter screening would be implemented, even if it means longer delays for awarding US visas to visitors.
“These are the things we are thinking about. But over there we can ask them for this kind of information and if they truly want to come to America, then they will cooperate. If not, next in line.”