Troy Miller, the top official at U.S. Customs and Border Protection during most of President Joe Biden’s term, is preparing to retire at the end of December, according to an email sent to agency staff Tuesday. He is a 31-year veteran of the agency.

President Joe Biden is facing mounting pressure from Democratic lawmakers and allies to extend protections to immigrants in the United States amid party fears over President-elect Donald Trump’s promise of mass deportations.

The document will not be published due to the "sensitivity of some of its findings," the officials, who spoke on condition of anonymity under White House ground rules, told the Associated Press.