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 Columbia student, was arrested by ICE in March over his involvement in pro-Palestine activism despite being a permanent resident. Citing a Cold War-era law, administration officials claimed Khalil’s presence in the country is detrimental to the US’s foreign policy interest.

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.