Students gathered in New York City's Washington Square Tuesday to protest the arrest of Mahmoud Khalil, a pro-Palestinian activist at Columbia University who was detained by U.S. Immigration and Customs Enforcement agents this past weekend.

Mahmoud Khalil, a 29-year-old legal resident of the United States, was arrested and detained by federal agents Sunday, after his green card was revoked by the Trump administration.

The White House complained that Columbia University is refusing to help federal agents find people being sought as part of the government’s effort to deport participants in pro-Palestinian demonstrations.