The federal government is taking another step it says would make the US homeland safer from terrorism. US border authorities are proposing that millions of tourists entering the country each year reveal their social media identities.

The proposal from US Customs and Border Protection, announced last week in the Federal Register, would add a line to the online or paper form that US-bound visitors must fill out if they don't have a visa and plan on staying for up to 90 days for vacation, business, or other affairs. The agency says travelers coming to the US under the Visa Waiver Program won't be forced to disclose their social media handles, but leaving it blank obviously could raise red flags.

Here's what will be asked: "Please enter information associated with your online presence—Provider/Platform—Social media identifier." This field doesn't call for additional information such as passwords, but it's likely to yield many if applicants aren't paying attention and overshare.

"It will be an optional data field to request social media identifiers to be used for vetting purposes, as well as applicant contact information," the government said on the Federal Register. "Collecting social media data will enhance the existing investigative process and provide DHS 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 agency said the form travelers fill out enables "the Department of Homeland Security (DHS) to perform its mission related to the screening of alien visitors for potential risks to national security and the determination of admissibility to the United States."

The proposal comes six months after President Barack Obama signed the Visa Waiver Program Improvement and Terrorist Travel Prevention Act of 2015 that added other questions to US-bound travelers. The form now asks applicants about which countries they've been to after March 1, 2011. It also asks which countries they are nationals or citizens of and for which nations they have passports and Global Entry codes.

The government is taking comments on the proposal until August 22. They can be snail-mailed to US Customs and Border Protection, Attn: Paperwork Reduction Act Officer, Regulations and Rulings, Office of Trade, 90 K Street NE., 10th Floor, Washington, DC 20229-1177.