The U.S. Attorney’s Office for the Southern District of New York is planning to weigh in on constitutional issues raised by federal lawsuit filed by President Donald Trump Sept. 19 challenging a Manhattan grand jury subpoena seeking his tax returns, according to a notice sent Monday by prosecutors to the judge presiding over the case.

Trump sued New York County District Attorney Cyrus Vance Jr. in the Southern District of New York, calling the subpoena, which was issued to Mazars, an accounting firm that has performed work for Trump and his businesses, a “campaign to harass the president” and making the constitutional argument that he should be immune to state prosecution as long as he is in the White House.