The Trump administration has said it wants to start collecting the social media history of nearly everyone seeking a visa to enter the US.
The proposal, which comes from the state department, would require most visa applicants to give details of their Facebook and Twitter accounts.
They would have to disclose all social media identities used in the past five years.
About 14.7 million people a year would be affected by the proposals.
The information would be used to identify and vet those seeking both immigrant and non-immigrant visas.
Applicants would also be asked for five years of their telephone numbers, email addresses and travel history. They would be required to say if they had ever been deported from a country, or if any relatives had been involved in terrorist activity.
The proposal would not affect citizens from countries to which the US grants visa-free travel status - among them the UK, Canada, France and Germany. However, citizens from non-exempt countries like India, China and Mexico could be embroiled if they visit the US for work or a holiday.
Officials defended the proposal by saying it would help to identify potential extremists.
Social media came under scrutiny after the shootings in 2015 in San Bernadino, California, in which 14 people died. The authorities said they had missed signs of radicalisation in messages on a messaging platform sent between the attackers.
Under rules brought in last May, officials were told to seek people's social media handles only if they felt "that such information is required to confirm identity or conduct more rigorous national security vetting", a state department official said at the time.
The tougher proposal comes after President Trump promised to implement "extreme vetting" for foreigners entering the US, which he said was to combat terrorism.
"Maintaining robust screening standards for visa applicants is a dynamic practice that must adapt to emerging threats," the state department said in a statement, quoted by the New York Times.
"We already request limited contact information, travel history, family member information, and previous addresses from all visa applicants. Collecting this additional information from visa applicants will strengthen our process for vetting these applicants and confirming their identity."
