The president escalated his feud with Harvard on Wednesday by signing an order that deems the entry of the university’s international students into the U.S. a national security threat.

President Donald Trump signed a proclamation to suspend international visas for new students at Harvard University, the White House announced Wednesday, in a dramatic escalation of its efforts to block foreigners from enrolling at the elite university.

President Donald Trump is moving to block nearly all foreign students from entering the country to attend Harvard University, his latest attempt to choke the Ivy League school from an international pipeline that accounts for a quarter of the student body.