UPDATE: A judge has blocked the federal government from deporting citizens of seven countries who were detained at U.S. airports over the past day or so as a result of an executive order President Donald Trump issued Friday. Click here for more.

President Donald Trump has billed his executive order cracking down on immigration and refugees as a way to keep out “radical Islamic terrorists.”


But in the long run, it could hamper Americans trying to travel abroad and make it harder for the United States to deport criminals to other nations. Already, Iran has promised to "reciprocate" over what it called a "flagrant insult to the Muslim world."

While there are many long-term implications of the multi-faceted order, for many individuals the fallout was much more immediate.

Many permanent legal U.S. residents were told they could not set foot on U.S. soil as they returned from trips abroad — a shock to a group that’s just one step short of American citizenship. Some travelers were barred from boarding planes to the United States. Two Iraqis, one who had obtained a visa for helping U.S. troops and another trying to reunite with his refugee family, reached a New York airport but were prevented from entering the U.S., sparking a lawsuit . Certain people with dual citizenship are now barred from the U.S., possibly indefinitely, even if they once could visit without a visa. Companies such as Google and Microsoft spoke out against Trump’s order, saying it would hurt many of their employees.

“The executive order is an unprecedented and discriminatory assault on whole groups of people that plays to our worst fears,” said Royce Murray, policy director at the American Immigration Council. “It’s not unreasonable to expect backlash from countries around the world who want to show the United States that this is the wrong way to go.”

The order that Trump signed Friday has of number of elements: an indefinite ban on Syrian refugees; a temporary ban on all refugees; a temporary halt to the admission of people from seven Muslim-majority countries; and a directive that religious minorities, which by implication means Christians in many cases, get priority among refugees eventually admitted to the United States. Some parts of the order, such as the targeting of the seven countries, appear at first to be temporary. But they could stay in effect indefinitely if Trump’s demands, such as increased cooperation from often hostile or incapacitated governments, are not met.

Trump and his aides say such “extreme vetting” is necessary to prevent Americans from being attacked by terrorists trying to infiltrate the United States. The president’s order even includes language saying the U.S. should not admit anyone who engages in “acts of bigotry,” suggesting he’ll be pushing an ideological test on would-be visitors.

Opponents of the order say it amounts to a “Muslim ban” that will enhance terrorist recruitment, anger U.S. allies and hurt some of the world’s most vulnerable people. They also note that refugees, the most heavily screened group of people allowed to enter the United States, have almost never been accused of terrorist attacks.

The overall impact of the order could reach well beyond the Muslim world, however, affecting global businesses, universities and tourism, not to mention a host of bilateral relationships. Trump also imposes tough new conditions for the vetting of visitors from most countries in the world, including places such as China.

The president has directed the relevant Cabinet agencies to review the vetting process involved for citizens from all countries where visas are required to travel to the United States, in order to make sure that those countries are providing enough information to help the U.S. review the visa applications. Countries that the Trump administration decides are not offering enough information will be told to do so. If they don’t step up their cooperation, their citizens will be prohibited from traveling to the United States.

The president is expected to make a proclamation of which countries fall on the prohibited list within three months. During that period, citizens of seven countries — Iran, Iraq, Syria, Sudan, Somalia, Libya and Yemen — are prohibited from entering the United States unless their countries meet the same standards.

But a country such as Iran, which does not have diplomatic relations with the United States, is unlikely to ever meet Trump’s demand. The government of Yemen, mired in a war that has drawn in the United States, is too hobbled to do much of anything. And even other countries, in Latin America, for instance, may bristle at Trump’s demands for more data. Muslim countries not on the list of seven targeted also may feel a need to act out of solidarity.

Because visa programs are, in theory, supposed to be reciprocal, many of the affected countries could decide to take their frustrations out on American travelers.

It’s unlikely many countries will flat out bar Americans, who often are a critical source of tourism revenue. But they might slow down the visa issuance process, impose their own ideological tests during visa interviews, or take other steps to retaliate. Several years ago, an outraged Brazil imposed fingerprinting and photographing requirements for American visitors after its citizens were subject to similar treatment by the United States, an episode that soured relations and led to hours of headaches for even some U.S. diplomats.

Separately, some countries, such as China, may curtail cooperation on other fronts, such as accepting Chinese citizens ordered deported from the United States, some of whom may have committed crimes. Even Iran, which does take small numbers of deportees back every year, may now stop doing so.

According to Iranian state media, the country's foreign ministry issued a lengthy statement slamming Trump's order as "a great gift to extremists and their sponsors" and promising to "reciprocate."

“People need to realize there’s an ebb and flow to these things,” said Leon Fresco, an immigration attorney and former Department of Justice official. “All visas, they work on this basis of reciprocity. Brazil makes us get visas to go to Brazil because we make them get visas to come here.”

Countries in Europe and other strong U.S. allies could also be affected because the order also covers people with multiple nationalities. Many of those countries are part of what's known as the Visa Waiver Program, which allows their citizens to temporarily visit the United States without a visa. But the State Department confirmed Saturday that if any of those same citizens also hold nationalities from the seven Muslim-majority countries singled out by the order, they, too, will be barred from entering the United States.

Trump’s order also gets rid of a program that allows some visa applicants to skip the in-person interview process, meaning the overall application process will now take longer and require more U.S. resources. Trump also demands the imposition of a uniform screening procedure for all immigration programs that includes “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.” It’s not clear what that means in practice or how to define “national interest," but that standard also gives some wiggle room to the government. The order states that the secretaries of state and homeland security can admit certain individuals “on a case-by-case basis” if they determine it is in “the national interest.” Such determinations, however, could take significant time to reach.

One of the most surprising results of the new order involves so-called green card holders, who are legal U.S. permanent residents with protections in U.S. law. Obtaining permanent residency, a step just short of citizenship, usually requires living for several years in the United States and establishing roots. But according to several advocacy groups, many green card holders returning from trips abroad were stopped at the airport and told they could not re-enter the United States.

A senior Trump administration official said Saturday that the ban on entry will apply to U.S. permanent residents who hail from the seven specifically targeted countries and who were trying to return to American after trips abroad. Such individuals will have to go through a review process and be evaluated on a case-by-case basis before being admitted back to the United States.

It was not clear what this additional screening process would entail, but the stance puzzled legal observers, who said it appeared to target the permanent residents simply because they decided to travel.

“There’s nothing in the immigration code that permits a lawful permanent resident to be denied entry into the United States on the basis of travel to any specific country,” Fresco said.

Private businesses and American universities could also be heavily affected by the new rules. Businesses who count on foreign workers could find their productivity affected if visa rules keep people from traveling or being allowed to work for them. Universities with large numbers of foreign students — a surprising number of whom come from the Muslim world — could see their revenues shrink if such students are barred. Even if some of those students are able to get visas, it could take so long they may not be able to start the school year on time.

The technology sector, which relies heavily on visa-holding foreign nationals, is especially alarmed. A spokesman for Microsoft said the company is “actively working” with affected employees “to provide legal advice and assistance.” According to Bloomberg News , Google ordered traveling staffers possibly impacted by the executive order to immediately get back to the United States. More than 100 Google employees are thought to be affected by Trump’s act, the company’s CEO is reported to have said.

Facebook founder Mark Zuckerberg on Friday released a statement urging the Trump administration not to overreach in its immigration crackdown. “We need to keep this country safe, but we should do that by focusing on people who actually pose a threat,” Zuckerberg said. “Expanding the focus of law enforcement beyond people who are real threats would make all Americans less safe by diverting resources.”

Democratic Sen. Jeanne Shaheen of New Hampshire was among several lawmakers furious over how the order effectively bars the admission of thousands of Iraqis who have served as translators and in other capacities for U.S. troops and officials. Such Iraqis often must endure years of screening as well as threats from militants while awaiting permission to go to America.

“Discriminating based on religion and nationality severely undermines the local alliances and trust established by our troops and diplomats in the field,” Shaheen argued.

A number of legal challenges are expected to the order, but each faces a tricky path. The U.S. president, and the U.S. government as a whole has tremendous leverage in who it allows into the country, not least because constitutional protections such as freedom of religion don't necessarily apply to foreigners.

But as they digested the executive order starting on Friday, several leaders of advocacy organizations as well as members of agencies such as the State Department said it appeared the Trump administration had not fully thought through the implications of what it was imposing. The president's aides had done little, if any, consulting with top policy-makers and lawyers from the various agencies now in charge of implementing the proposal.

Greg Chen, advocacy director for the American Immigration Lawyers Association, said Saturday morning that people across the government were trying to figure out how the order works.

"I have spoken with government officials in the relevant agencies who were not aware of the specifics of this executive order until late last night," he said, "when the entire world learned what was involved."

Tony Romm, Tara Palmeri and Seung Min Kim contributed to this report.