The Trump administration’s use of an obscure portion of immigration law to detain and attempt to deport pro-Palestinian activist Mahmoud Khalil is likely unconstitutional, according to an order issued Wednesday by a federal judge in New Jersey.

Khalil, a legal U.S. resident, was detained by federal immigration agents on March 8 in the lobby of his university-owned apartment, the first arrest under President Donald Trump’s widening crackdown on students who joined campus protests against Israel’s war in Gaza.

The former Columbia student and pro-Palestinian activist remains in detention despite a federal judge’s partial ruling in his favor.