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.

Vance's lawyers have pointed out that a grand jury subpoena does not mean the president will necessarily be charged with any crimes and that grand juries typically have wide-ranging investigative powers. They also argued that the case should have been filed in state court since it was taking issue with a state subpoena.

The first hint of federal prosecutors' involvement came late Sept. 24, hours before attorneys representing Trump and Vance were scheduled for a hearing in the courtroom of U.S. Senior District Judge Victor Marrero.

Southern District U.S. Attorney Geoffrey Berman filed a letter that night supporting a temporary restraining order, saying it would give his office time to decide whether to participate.

He asked the court to prohibit enforcement of the subpoena "to preserve the status quo while the Court has the opportunity to receive a more complete presentation regarding the weighty constitutional issues raised by plaintiff's suit."

Marrero set a deadline Monday for the U.S. Attorney's Office to say whether it would participate and a filing deadline Wednesday.

Berman sent a one-paragraph notice to Marrero Monday, confirming that prosecutors will file papers by 5 p.m. Wednesday.

Meanwhile, lawyers for Trump and Vance have agreed that Vance's office will not enforce the subpoena until 1 p.m. Oct. 7 or 1 p.m. on the day that falls two business days after Marrero rules on pending motions, whichever is sooner.

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