Manhattan District Attorney Alvin Bragg is suing to prevent House Republicans from subpoenaing Mark Pomerantz, a former assistant DA who was involved in the investigation of former President Donald Trump.

In a 50-page lawsuit, Bragg slammed House GOP efforts to compel Pomerantz’s testimony as a “brazen and unconstitutional attack” and described it as a “campaign of harassment in retaliation for the District Attorney’s investigation and prosecution of Mr. Trump.” Bragg is also seeking a court order to bar Pomerantz from complying with the subpoena.

The subpoena is an extraordinary escalation of the clash between the House Judiciary Committee and Bragg’s office, which is prosecuting the former president for allegedly falsifying business records to cover up a hush money scheme. The Judiciary panel’s chair, Ohio Republican Jim Jordan, did not immediately return a request for comment.