BOSTON (AP) —The presidents of several universities on Sunday issued scathing attacks of Trump’s executive order halting immigration from seven Muslim-majority nations. Many said it’s already disrupting research and academics for their scholars, while some suggested they would defy the ban as far as legally possible.

The Association of American Universities, which represents 62 schools, urged Trump to reverse the order and said it will only steer top scholars to countries that compete with the United States.

Mitch Daniels, the president of Purdue University and a former Republican governor of Indiana, called the order “a bad idea, poorly implemented,” and called on Trump to revoke it.

The ban, which blocks immigrants from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen, has been put on hold after federal judges in New York, Massachusetts, Virginia and Washington state stepped in. But some students and scholars from those countries remain caught in legal limbo, stranded while traveling abroad or visiting home during the recent holiday break.

Ata Anzali, an assistant professor of religion at Vermont’s Middlebury College, has been living in his home country of Iran since last summer to conduct research. His family booked flights that would have brought them back to the U.S. just before noon Sunday, but Anzali changed his mind at the last minute. He said he canceled two flights because he feared his children might get snarled by the travel ban.

“I don’t want my kids to go through this traumatic experience of being detained or deported,” Anzali told The Associated Press in a telephone interview from Iran. “This is causing so much confusion, what are we supposed to do?”

Yale University doctoral student Ali Abdi, who is from Iran, left the U.S. days before the order was signed to conduct research in Afghanistan. Now he doesn’t know if he can return.

“I cannot go to Iran, my home country, because I’ve been a human rights activist over the past 10 years and I might face some sort of persecution,” he said. “I’m in a situation where it seems I am neither welcome by the Iranian government or the American government.”

A Stanford University student from Sudan who is a legal resident in the U.S. was detained for hours after arriving in New York on Friday but later allowed in.

“An unfortunate consequence of the new policy appears to be that students and scholars from designated countries are, for the moment, effectively detainees in this country,” Stanford President Marc Tessier-Lavigne and other leaders from the school wrote in a letter.

University of Massachusetts President Marty Meehan said several students and faculty members were traveling abroad when the order was signed, including two professors from Iran who were temporarily detained at Logan Airport in Boston even though they’re permanent U.S. residents.

“This is not the country we promised to them when we invited them to study, teach and conduct research here,” Meehan wrote.

Students and scholars from several other colleges also have been stuck, including from Harvard University, the Massachusetts Institute of Technology and Clark Atlanta University.

More than 17,000 students from the seven counties affected by the ban studied at American colleges last year, according to data from the State Department and the nonprofit Institute of International Education. More than 12,000 of those were from Iran.

As spring break approaches, some international students were planning to visit home or take academic trips abroad. But now, many colleges are urging them to reconsider.

Schools including Johns Hopkins University in Baltimore and Tufts University in Boston guided students from nations under the ban to avoid all travel outside the U.S. Many are advising to students to determine whether it’s safe to travel.

On social media, some schools received praise Sunday for saying they would do everything in their power to protect immigrants on campus.

The University of Michigan said its campus police don’t ask about immigration status and don’t partner with federal officials to enforce immigration laws. Duke University said it “cannot and will not share confidential student records with law enforcement agencies — local, state, or federal — without a subpoena.”