How can the US government stop Harvard from enrolling international students?

The Trump administration wants to halt Harvard University from enrolling international students. But how can the federal government dictate which students a private university can and cannot enroll?

The government has enormous power over who comes into the United States, and who doesn't. For college and universities, the Department of Homeland Security has a vast system just to manage and track the enrollment of the hundreds of thousands of international students studying across the country at any given time.

But a school needs government certification to use this database, known as SEVIS, for the Student and Exchange Visitor Information System. And this vulnerability is what the Trump administration is exploiting against Harvard.

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Homeland Security says that effective immediately, it has revoked a certification that allows Harvard to have access to SEVIS. Oddly enough, the students may still have valid visas. But Harvard is no longer able to log them into this all-important database.

The announcement was a significant escalation in the administration's efforts to pressure Harvard to fall in line with the president's agenda.

Here's what we know so far.

How does Harvard use the SEVIS database?
For each international student, Harvard inputs data into SEVIS to show that a student is enrolled full time, and thus meeting the terms of the visa that the student was issued.

The system is overseen by U.S. Immigration and Customs Enforcement, an arm of Homeland Security, which announced the termination Thursday.

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At Harvard, more than a quarter of its total student body, or 6,800 students, come from other countries.

How are international students at Harvard affected?
The SEVIS termination for Harvard would mean that all foreign students at the school would be in limbo. The students would, en masse, become deportable immediately, unless they transferred to another school, or unless a court intervened to block the termination by Homeland Security. Students who took no action to enroll elsewhere would be violating the terms of their status and subject to removal.

After graduating, international students have 60 days from the end of their program to leave the United States or adjust their immigration status, by obtaining a job, for example.

Students who are returning to university programs typically can remain in the country during summer breaks because they are still enrolled for the coming term.

But if SEVIS is terminated for Harvard, it's unclear if students who would otherwise be returning would still be granted the summer grace period.

The current spring term at Harvard ends Monday, according to the university's calendar.

But don't international students have visas?
It does not appear that Homeland Security revoked the student visas of Harvard's international students. That means, in theory, they could leave or stay for the summer. They could go back to their home countries, potentially, and return to attend another school. Much of this is still unclear.

What might Harvard do next?
Harvard could go to court to try to challenge its SEVIS termination.

Carl Tobias, an expert on the federal courts at University of Richmond School of Law, said that Harvard would very likely sue in federal court in Massachusetts asserting that the actions of the Homeland Security secretary, Kristi Noem, violated the law by effectively dismantling the university's international program and preventing it from recruiting students from around the globe.

"Harvard will argue that the actions of the secretary are arbitrary and capricious," Tobias said. "A court is likely to find that she lacks the power to eliminate its program for international students."

Stacy Tolchin, an immigration lawyer who represents international students, said that the university would have a "clear case challenge for retaliation from DHS based on First Amendment-protected activities."

This article originally appeared in The New York Times.