The chief of the criminal division at the U.S. Attorney's Office for Washington, D.C. abruptly resigned Tuesday amid pressure from top Trump Justice Department appointees to freeze assets stemming from a Biden administration-era environmental initiative, sources familiar with the matter told ABC News.

       A resignation letter sent to the office's employees by prosecutor Denise Cheung did not detail specific reasons for her sudden departure from the office, but encouraged prosecutors to continue adhering to the Constitution.

       "Please continue to support one another, to fulfill your commitment to pursuing justice without fear or prejudice, and to be kind to, and take care of, yourselves," Cheung said. "You are the resource our nation has."

       The US Department of Justice (DOJ) headquarters building in Washington, D.C.

       STOCK PHOTO/Adobe

       Sources familiar with the matter told ABC News that Cheung was under pressure from Department of Justice (DOJ) leadership, including acting Deputy Attorney General Emil Bove and interim U.S. Attorney Ed Martin, to launch a formal criminal investigation into an Environmental Protection Agency (EPA) funding initiative pursued under the Biden administration, a request Cheung believed lacked the proper predication to initiate a grand jury investigation.

       MORE: Acting US Attorney for DC initiates 'review' of office's Jan. 6 investigation

       EPA Administrator Lee Zeldin has previously addressed with DOJ their effort to rescind contracts tied to the so-called Greenhouse Gas Reduction Fund. DOJ's intervention in the process can only come when prosecutors can credibly allege that the funds are tied to a crime.

       Cheung's resignation letter comes just one day after President Trump announced Martin as his nominee for U.S. attorney for Washington, D.C. amid a wave of controversial actions and statements by Martin in his weeks leading the office, actions that have led to growing consternation among career prosecutors.

       Ed Martin speaks at an event hosted by Rep. Matt Gaetz, R-Fla., at the Capitol in Washington, June 13, 2023.

       Amanda Andrade-Rhoades/AP

       As ABC News has previously reported, Martin has represented defendants charged in connection with the Jan. 6 riot at the U.S. Capitol and was on Capitol grounds himself on that day, though it's unclear whether he ever entered areas officially designated as restricted.

       A Justice Department spokesperson did not immediately respond to an ABC News request for comment.