Foreign students must leave the United States if their school’s classes this fall will be taught completely online or transfer to another school with in-person instruction, the US Immigration and Customs Enforcement (ICE) agency announced on Monday.

It was not immediately clear how many student visa holders would be affected by the move, but foreign students are a key source of revenue for many U.S. universities as they often pay full tuition.

ICE said it would not allow holders of student visas to remain in the country if their school was fully online for the fall. Those students must transfer or leave the country, or they potentially face deportation proceedings, according to the announcement.

Colleges and universities have begun to announce plans for the fall 2020 semester amid the continued coronavirus pandemic. Harvard University on Monday announced it would conduct course instruction online for the 2020-2021 academic year.

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The ICE guidance applies to holders of F-1 and M-1 visas, which are for academic and vocational students. The State Department issued 388,839 F visas and 9,518 M visas in fiscal 2019, according to the agency’s data.

The guidance does not affect students taking classes in person. It also does not affect F-1 students taking a partial online course-load, as long as their university certifies the student’s instruction is not completely digital. M-1 vocational program students and F-1 English language training program students will not be allowed to take any classes online.

President Donald Trump’s administration has imposed a number of new restrictions to legal and illegal immigration in recent months as a result of the coronavirus pandemic.

In June, the administration suspended work visas for a wide swath of nonimmigrant workers that it argued compete with US citizens for jobs. The administration has also effectively suspended the admission of asylum seekers at the southern border with Mexico, citing coronavirus-related health risks as justification.