PresidentDonald Trumpis moving to block nearly all foreign students from entering the country to attend Harvard University, hislatest attemptto choke the Ivy League school from an international pipeline that accounts for a quarter of the student body.

In an executive order signed Wednesday, Trump declared that it would jeopardize national security to allow Harvard to continue hosting foreign students on its campus in Cambridge, Massachusetts.

“I have determined that the entry of the class of foreign nationals described above is detrimental to the interests of the United States because, in my judgment, Harvard’s conduct has rendered it an unsuitable destination for foreign students and researchers,” Trump wrote in the order.

It’s a further escalation in the White House’s fight with the nation’s oldest and wealthiest university. A federal court in Boston blocked the Department of Homeland Security from barring international students at Harvard last week. Trump’s order invokes a different legal authority.

It stems from Harvard’s refusal to submit to a series of demands made by the federal government. It has escalated recently after the Department of Homeland Security said Harvard refused to provide records related to misconduct by foreign students.

Harvard says it has complied with the request, but the government said the school's response was insufficient.