The Trump administration is moving to expand social media checks to cover Chinese citizens traveling to the U.S.

U.S. Customs and Border Protection officials are proposing to ask Chinese visitors to disclose their social media “handles” or other identifiers on common social media platforms like Twitter and Facebook. The question would be asked online as part of an electronic system Chinese holders of long-term U.S. business and visitor visas use to advise of upcoming travel.

Answering the question would be “optional,” CBP said in a notice set for publication Tuesday in the Federal Register. Those who don’t wish to answer will have their travel requests processed “without a negative interpretation or inference,” the notice said.

The Obama administration rolled out a similar, voluntary, social-media screening effort late last year for travelers eligible to enter the U.S. through the Visa Waiver Program, which includes many European countries and other highly-developed nations.

The move to cover Chinese visitors in the social-media-focused screening comes as Trump administration officials are publicly discussing far more intrusive steps to vet foreigners seeking to enter the U.S., including asking for social media passwords.

Homeland Security Secretary John Kelly told a Congressional hearing last week that the administration was considering asking visitors from some countries to turn over those codes as part of an attempt to screen out potential terrorists.

“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,” Kelly said.

Online privacy advocates and technology firms are deeply wary of the security and privacy implications of that idea. Some activists are concerned that expanding the current social-media collection effort is the Trump administration’s first formal step in that direction.

“This is the first concrete proposal that we’ve seen” under Trump, said Emma Llanso of the Center for Democracy and Technology.

Llanso warned that U.S. requests or demands for social media profiles will almost certainly lead to similar demands from other countries.

“So many countries around the world grant visas or visa waiver on a reciprocity basis, if the U.S. starts demanding greater information from different countries or different groups of travelers, we should not be surprised at all if other governments do the same thing,” Llanso said.

It’s unclear how helpful the information the U.S. receives through social-media screening is. Obviously, people looking to hide something could decline to provide their social media handles or “forget” to list one of them. The query alone could also prompt some individuals to scrub their profiles or change privacy settings to hide them. U.S. surveillance systems could potentially penetrate such protections, but the new notice says CBP officers will review postings “consistent with the privacy settings the applicant has chosen to adopt.”

The initial iteration of the program to collect social media handles asked travelers about profiles on sites like Facebook, Google+, Instagram, LinkedIn and YouTube. However, residents of China tend to use other social media platforms, in part because U.S. sites are often blocked by the Chinese Government.

A CBP spokeswoman had no immediate comment on whether Chinese social media platforms would be included.