When President Donald Trump issued his executive order on immigration last week, it was the travel ban on seven Muslim-majority countries that dominated headlines—leaving hundreds of people in limbo, provoking airport protests, and raising questions about whether the U.S. was targeting religion in the guise of a new security rule.

But immigration lawyers who have read the order carefully are now increasingly concerned that one of its provisions could have much wider repercussions, affecting literally every foreign visitor to America, from tourists to diplomats.

The little-noticed section, appearing immediately after the travel ban, calls for the government to develop a “uniform screening standard and procedure” for all individuals seeking to enter the United States. As written, it appears to require all visitors to go through the same vetting measures, regardless of where they come from or how long they intend to stay.

If interpreted as broadly as it’s written, “It would basically shut down tourism,” said Stephen Legomsky, the former chief counsel for U.S. Citizenship and Immigration Services during the Obama administration.

Trump’s executive order, issued last Friday, has already been criticized as hastily drafted and confusing, and the White House has already loosened up one portion of it, allowing green card holders currently overseas to re-enter the U.S.

But little attention has focused on section four, which directs federal officials to implement a “uniform screening standard and procedure” as part of the “adjudication process for immigration benefits” for all individuals seeking to enter the United States. In immigration parlance, “immigration benefits” refers to any permission granted a foreign visitor, from full-scale refugee resettlement to a passport stamp for tourists visiting Disneyland. That wording is about as broad as it can get, lawyers said, and if taken literally would include every single foreigner coming to the United States. “[It] is basically everything,” said Dan Stein, the president of the Federation for American Immigration Reform (FAIR), a group that supports reducing immigration levels.

“What they are talking about doing has scared the shit out of my members, about the lack of guidance and lack of clarity,” said Ben Johnson, the head of the American Immigration Lawyers Association.

The implications of the order as written are so extreme that most lawyers are convinced that the Trump administration will not adhere to its literal meaning; as with other sections of the order, they expect the White House to stray from the drafted language. But such uncertainty has left lawyers baffled about what the interpretation will actually look like, and wondering whether Trump and his top advisors really do intend to upend the U.S. immigration system—and possibly disrupt global travel altogether.

Said Kathleen Campbell Walker, an immigration attorney in Texas and former head of the American Immigration Lawyers Association, “Good Lord, I’ve been doing this for 31 years and I’m trying to figure out what this means.”

“Do they want to create, like we have for refugees now, a two-year process [for everyone looking to enter the U.S.] that involves multiple screenings and re-screenings and vetting by every single security agency?” said Donald Kerwin, the executive director of the Center for Migration Studies. “I don’t think so. I think that would shut down immigration to the United States.”

Former government officials from both parties pointed out that enforcing it would be virtually impossible with current resources, either forcing the administration to abandon the standard or dramatically reducing the number of foreigners who travel to the U.S.

“They just can’t physically do it. It really can’t happen,” said Legomsky, who also pointed out that if they did, it would cause blowback that would hurt American travelers as well. “Other countries would reciprocate some of our constraints on U.S. citizens seeking to travel,” he said.

“I don’t know what they mean by that,” said Robert Divine, the former chief counsel at U.S. Immigration and Custom Services during the George W. Bush administration. A uniform standard is so resource-intensive, he said, as to be completely unworkable. “They’ll find out that there aren’t enough resources to go around and the nation still needs the wheels to turn and people to come here. It’ll be a painful process of realization.”

More than 10 million people traveled to the U.S. on a visa in 2015—including immigrants and nonimmigrants—while tens of millions visited the United States without a visa. The section calls for the secretary of state, secretary of homeland security, director of national intelligence and FBI director to develop a “uniform screening standard and procedure” for all of them. That could slow travel to the U.S. to a crawl, upending the tourism industry and creating massive headaches for companies with foreign employees who frequently travel to the U.S. Foreign airline employees would have to go through significant vetting procedures every time they enter here.

So what does Trump really mean by a “uniform screening standard and procedure”? Immigration lawyers weren’t sure. Given Trump’s promise of “extreme vetting,” it could be very stringent, requiring an in-person interview, detailed documentation, medical histories and biometric testing such as fingerprints, among other information. The section suggests, but doesn’t mandate, in-person interviews, a database of identity documents and forms with questions to identify fraudulent answers and to confirm the applicant’s identity. That would be a huge break from the current system, which adopts a risk-based approach where people considered to pose a greater risk to the U.S. undergo a more thorough and lengthy vetting process, and in which people travelling from any of 38 specified countries—allies like Britain, France and Australia—don’t need a visa to visit at all. Requiring those travelers to undergo the same vetting procedures as a refugee would create an enormous strain on foreign consulates and U.S. immigration authorities, effectively imposing tight new limits on how many people can visit the U.S. each year.

“It’s hard for me to imagine a screening procedure that is rigorous enough for people who are coming here permanently that, with present resources, we could come even close to using for the 50 million tourists entering our territory,” said Legomsky. He added, “Either the language is hopelessly incompetent or they really do mean that there has to be one uniform screening standard that would be unworkable in practice.”

Unlike other sections of the order, section four doesn’t mention an exception for certain visa holders, including those with diplomatic visas, and it does not grant the secretary of homeland security, or any other official, the authority to waive the screening on a case-by-case basis. Based on the text, then, foreign heads of states, including those of allies like Britain’s Theresa May and Germany’s Angela Merkel, would have to go through the same vetting process as every other foreigner seeking to enter the U.S.

The pragmatic view of the order is that the final policy would naturally include plenty of exemptions; Stein, the head of FAIR, argued that the order should not be read to mean that every foreigner would undergo the same vetting process but instead that vetting would context-specific. “There are not unlimited resources,” he said. “So therefore, one would assume that they are going to use a rule of reason in what they mean by ‘uniform’.” He continued, “Spinning out scenarios of an impractical uniformity sounds kind of foolish, because that’s not the real world.”

Most immigration lawyers agreed with Stein that the Trump administration would ultimately interpret “uniform” to mean context-specific—that is, not really uniform.

“I don’t think this limits itself to one size has to fit all,” said Michael Neifach, a lawyer who held senior positions at DHS during the Bush administration. “But this is very broad language. You’ve seen with the other sections of the executive order, it’s subject to modification.”

The White House did not respond to multiple emails asking how to interpret the section. The office of the director of national intelligence said “it did not have anything to offer on this question” and the FBI directed requests to Department of Homeland Security, which did not respond to emails and calls asking for clarification. A State Department official said the new policy was underway, but without offering specifics: “Working closely with the Department of Homeland Security, we are implementing the Executive Order. We will announce any changes affecting travelers to the United States as soon as that information is available.”

Experts are also concerned with the potential criteria that the order suggests should be included in a uniform standard. It suggests a “process to evaluate the applicant’s likelihood of becoming a positively contributing member of society and the applicant’s ability to make contributions to the national interest,” wording that lawyers said was impossible to decipher. “What does that mean?” asked a Democratic aide. “Who is a positively contributing member of society?” The order also suggests that the standard include some mechanism to determine whether the applicant “has the intent to commit criminal or terrorist acts” in the U.S.

The order lays out no timetable for when the uniform standard should be implemented, but directs the secretary of homeland security to submit three reports—within 60 days, within 100 days and within 200 days—on the departments’ progress complying with the order.

Even with a less extreme interpretation, immigration experts expect that changes to the vetting process will still affect nearly everyone coming to the U.S. Trump advisors Steve Bannon and Stephen Miller, two of the leading authors of the executive order, have shown interest in not just reducing the number of undocumented immigrants in the U.S. but reducing the flow of legal immigrants as well. The travel ban, controversial as it is, does not go far towards accomplishing that goal, since it is largely restricted to seven countries that send relatively few people to America. But a broader tightening of the vetting process could be far more effective, gumming up the entire system and slowing the flow of all arrivals.

To immigration restrictionist groups like FAIR, such a crackdown on immigration flows has long been needed for America’s national and economic security. Stricter vetting measures are necessary even for people coming from closely allied countries included in the Visa Waiver Program, they say, due to the fact that more than a million refugees have migrated to Europe, specifically Germany.

“If you are going to keep Schengen in place and keep the E.U. functioning,” said Stein, referring to the area of Europe with passport-free travel, “there is going to have to be a far more elaborate vetting process over the chaos that Merkel has been leading the last several years.”

Many immigration lawyers and former Obama administration officials are critical of that reasoning. Instead of making the country safer, they said, a uniform screening standard would waste limited resources on low-risk travelers, potentially allowing more high-risk ones to fall through the cracks. “That creates a bit more of a needle in a haystack problem,” said Betsy Cooper, a former attorney advisor at the Department of Homeland Security. “If you are treating every piece of hay like it could equally be a needle, it becomes a lot harder to find the needle.”

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