When President Trump signed an executive order Friday temporarily preventing citizens of seven predominantly Muslim countries from entering the U.S., a group of nonimmigrants was swept up in the ensuing chaos over who the ban would apply to: college students. Two undergraduates from the Massachusetts Institute of Technology, where spring semester classes don’t begin until next week, are among those who have been prevented from entering the U.S, according to the university. Although a federal court order from Massachusetts appears to allow the students temporary entry to the U.S., at the time of publication, MIT said it was still working to bring the two students back.

There were 47 students enrolled at MIT in the fall term from the seven countries called out by the order, according to the university’s registrar, but it’s far from the only university affected. Thousands of students from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen are currently studying or working on visas in the United States. The executive order banned citizens of the seven countries from entering the U.S. for 90 days and stopped all refugees from entering the country for 120 days.

COUNTRY STUDENTS Iran 12,269 Iraq 1,901 Libya 1,514 Syria 783 Yemen 599 Sudan 253 Somalia 35 Students in the U.S. from the seven countries in Trump’s executive order, 2015-16 Source: Institute of International Education

Of the seven countries, Iran sends the largest number of students to the U.S., 12,269 last academic year, and the 11th-most of any country in the world, according to the Institute of International Education, a nonprofit group that does an annual survey of foreign students in the U.S. That’s the largest number of Iranian students in the U.S. in 29 years, according to the institute, although there were more than 50,000 during the peak year of 1979-80, when Iran was the largest sender of international students to the United States.

Restricting students from these countries could have a negative impact on the U.S. economy, said Neil Ruiz, who studies the economic impact of migration and is the executive director of the George Washington University Center for Law, Economics and Finance. Using 2008-12 data, he found that two-thirds of foreign students study science and technology, often referred to as STEM, or business and marketing, with many staying on to work in the United States. This is important because there are not enough U.S.-born graduates prepared to work in STEM fields, a sector considered vital to the nation’s economic growth. Because the U.S. doesn’t track how many international students who study in the U.S. stay to work after graduation, Ruiz looked at graduates who received work authorization for a limited time post-graduation and found that more than 5,000 visas were granted from 2012 to 2015 to people from countries affected by the ban. Seventy-five percent were STEM majors, a group that, because of the workforce shortages, has historically been given priority for visa extensions.

These U.S.-trained graduates affect innovation and economic growth, Ruiz said. “We are the global hub for higher education in the world,” he said. “If we want to continue to be a great country, we have to continue to make sure that our higher-education system gets the best and brightest in the world, and Iran does provide some of our best and brightest.” He said he’s worried that Trump’s executive order will deter students from not only the seven countries, but others as well. “They will wonder, ‘Will we be on the list next?’” Ruiz said.

And there’s evidence that universities could be directly affected in other ways. Tuition from foreign students probably helped offset the effects of constricting state budgets that led to cuts to public university funding from 1996 to 2012, according to a recent study by a group of economists. State universities probably would have had to make larger increases to tuition of in-state students had it not been for an influx of international students, the authors concluded.

Concerns on college campuses go beyond the short-term impacts on travel, said Varun Soni, dean of religious life at the University of Southern California. USC has more than 11,000 international students, Soni said — more than any post-secondary institution in the U.S. except for New York University, including at least several dozen from the seven countries targeted by the executive order. “There’s a lot of anxiety about the uncertainty,” Soni said. “What does this mean for extending student visas? For the viability of completing degrees? For families attending graduation ceremonies?” Soni also said that a lack of freedom of movement affects the university’s ability to do research.

In a letter to the MIT community, President L. Rafael Reif praised the diversity of the university and expressed his concern over the order, writing: “Faculty, students, post-docs and staff from 134 other nations join us here because they love our mission, our values and our community. And — as I have — a great many stay in this country for life, repaying the American promise of freedom with their energy and their ideas.” Many other universities have spoken out, including by advising students and employees from the seven countries against international travel.

Universities may be right to focus on their entire international community. There is reason to believe the ban could grow. The executive order says that in the future, “the Secretary of State or the Secretary of Homeland Security may submit to the President the names of any additional countries recommended for similar treatment.”