Mayor Jesse Arreguín announced in a tweet Monday that Berkeley has filed an amicus brief to support California’s legal battle over the Trump administration’s immigration policies.

The Department of Justice filed a lawsuit against California in March, alleging that its sanctuary state laws are unconstitutional. The lawsuit focuses on AB 450, AB 103 and SB 54, three state bills that prohibit private citizens and local police from releasing information pertaining to immigration status to federal immigration authorities.

The lawsuit claims that the state’s sanctuary city laws violate the supremacy clause of the Constitution because the federal government has “undoubted, preeminent authority” over the state in regard to immigration.

Proud that Berkeley has joined more than two dozen key counties & cities in California in filing an amicus brief supporting the state in legal battle against Trump’s baseless anti-immigrant lawsuit. #ICEoutofCA #SB54 #DefendSanctuary

— Jesse Arreguin (@JesseArreguin) May 21, 2018

According to Berkeley law professor Leti Volpp, amicus briefs are filed by a party uninvolved in the case at hand, but who also “has a strong interest in the subject matter” and has relevant information to share before the court. Volpp noted that amicus briefs can have an impact on a case, yet such an occurrence is “unusual.”

Volpp said in an email that although she does not know the exact contents of the amicus brief, she speculates Berkeley’s brief will explain how AB 450, AB 103 and SB 54, the laws challenged by the federal government, benefit the residents of Berkeley.

Berkeley’s city attorney could not be reached for comment.

Arreguín said in an email that the city has “a long tradition” of protecting persecuted populations, a history that dates back to the Vietnam War. Arreguín added that all individuals living in the United States — including undocumented immigrants — have constitutionally protected basic rights.

“Berkeley is not alone: more than 600 cities and counties have become sanctuary cities,” Arreguín said in an email. “Ultimately, we believe that it’s cities that should decide on what makes good policy, not Washington politicians.”