In a cable sent Tuesday to U.S. embassies and consulates Tuesday, Secretary of State Marco Rubio halted the scheduling of new visa interviews for international students until the department releases guidelines for increased vetting of their activity on social media. Existing appointments may be kept and will proceed under current review guidelines, the cable said, but new guidance is expected in the coming days.

It came days after the Trump administration moved to block Harvard University from enrolling any international students, a decision that has been put on hold by a federal judge, pending a lawsuit.

Trump said Wednesday that Harvard, whose current student population is made up of more than a quarter of international students, should limit that percentage to about 15%.

“I want to make sure the foreign students are people that can love our country,” Trump told reporters in the Oval Office.

Earlier this year, U.S. Immigration and Customs Enforcement arrested and tried to deport students who had been involved in campus protests against the Israel-Hamas war. And the Trump administration abruptly terminated the legal status of thousands of international students before reversing itself and then expanding the grounds on which students can lose permission to study in the U.S.

The uncertainty raised by the suspension of the visa appointments will do further damage to the U.S. reputation as a destination country, said Fanta Aw, CEO of NAFSA, an association that represents international educators. Students generally commit to their program of study in late spring, meaning now would be peak time for students to schedule their visa interviews.

“International students and scholars are tremendous assets that contribute to U.S. preeminence in innovation, research, and economic strength,” Aw said in a statement. “Undermining their ability to study here is self-defeating. With these actions, the United States will alienate the very minds that fuel its success.”

The pause affects three categories of visas that cover a range of people seeking to study in the U.S. The largest category, F-1 visas, includes students who are enrolling at full-time accredited schools. Students participating in exchange programs enter on J-1 visas, and those enrolling in vocational or non-academic programs enter on M-1 visas.

The bulk of visa recipients are university students. However, visiting scholars, high school exchange students, summer program participants and boarding school students are also covered by the three affected visa categories.

Around 1.1 million international students were in the United States last year — a source of essential revenue for tuition-driven colleges. International students are not eligible for federal financial aid, and their ability to pay tuition often factors into whether they will be admitted to American schools. Often, they pay full price.

Visa applicants have been required to provide social media handles to the State Department since 2019. The cable did not indicate what kind of additional scrutiny the new guidelines would cover, but suggested the new reviews may be more resource-intensive.

“In light of potentially significant implications for consular section operations, processes, and resource allocations, consulate sections will need to take into consideration the workload and resource requirements of each case prior to scheduling them going forward,” the cable said.

The additional vetting will deter students from coming to the U.S., said Jonathan Friedman of PEN America, a literary and free expression organization.

“The details remain vague, but this policy risks upending the long-standing place of the U.S. as a beacon for intellectual and cultural exchange with the world,” Friedman said.

The move to cut off international enrollment at Harvard stems from a dispute with the Department of Homeland Security, which has demanded that it provide information about foreign students that might implicate them in violence or protests that could lead to their deportation. Harvard says it complied with the records request, but the agency said its response fell short.

On Wednesday, Trump said more scrutiny of Harvard’s students is necessary.

“They’re taking people from areas of the world that are very radicalized, and we don’t want them making trouble in our country,” Trump said.

The Trump administration has cut over $2.6 billion in federal grants for Harvard as it presses demands for changes to policies and governance at the Ivy League school, which the president has described as a hotbed of liberalism and antisemitism. Harvard has pushed back and filed a lawsuit against the administration.