How borders are drawn and enforced has far-reaching consequences, whether we live on either side of them or halfway across the world.

Name? Passport number? Twitter handle?

The US government this week started asking some foreign visitors to provide their social media account information before entering the country. The addition, which the Department of Homeland Security proposed in June and had open for comment until Aug. 22, went live Dec. 20, according to a Politico report. Rights��groups and technology companies had complained that the plan could constitute a violation of privacy.

Included in the Electronic System for Travel Authorization form, used by citizens of 38 countries to visit the US for up to 90 days without a visa, is an optional field that states: “Please enter information associated with your online presence.”

The fields include a drop-down menu where visitors select platforms including Twitter, Facebook, LinkedIn and Google+, among others, and another to fill in their “social media identifier.”

“The question was added as part of the agency’s efforts to enhance the vetting of travelers to the United States,” the Department of Homeland Security told Quartz.

The US government is trying to better screen for potential threats. One of the assailants in the San Bernadino, California, mass shooting in December 2015, Tashfeen Malik, had passed three background checks for her visa despite using social media to voice support for jihad. Her social media messages were created under a pseudonym and sent privately to her husband, Syed Rizwan Farook. The State Department had said that “obviously things went wrong” in the visa process.

But because filling out the form is optional it may not be effective in weeding out visitors who pose potential threats.