New State Department guidance on visa applications is adding to scrutiny of international students that has intensified under President Donald Trump, who has leveraged control of foreign enrollment to press his demands with American colleges.

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.

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.