In July, immigration attorney Daniel Kowalski published an internal Immigration and Customs Enforcement memo online. Now, the Trump administration has subpoenaed Kowalski demanding “all information” about how he obtained it, including “contact information for the source of the document,” the San Francisco Chronicle reported Wednesday.

The subpoena came from ICE’s Office of Professional Responsibility. (Pictured above: Acting ICE Director Ronald Vitiello.)

Kowalski, who also edits the professional journal Bender’s Immigration Bulletin, was defiant in his interview with the Chronicle.

“If they bring an action to enforce this so-called summons in federal District Court, I will resist it,” he told the paper. “I don’t know why they think … I would give up my source.”

The document Kowalski published relates to Attorney General Jeff Sessions’ decision in June that the U.S. would, in general, not grant asylum to those fleeing their countries due to domestic or gang violence. The ACLU sued in response.

Because Sessions, as attorney general, oversees the immigration court system, his decision impacted thousands of cases across the country. The document Kowalski leaked is a memo to ICE prosecutors about how to implement Sessions’ decision. The American Immigration Lawyers Association posted a copy of the memo online.

Omar Jadwat, director of the ACLU’s Immigrants’ Rights Project, told the Chronicle the administration’s subpoena was “obviously inappropriate” and “should be withdrawn.”