The Justice Department is targeting at least 300 foreign-born Americans to possibly revoke their citizenship as part of the Trump administration’s effort to ramp up denaturalization, according to a person familiar with the investigations.

A Justice Department official told NBC News the number was in the hundreds.

NBC News previously reported that the Trump administration was dramatically expanding an effort to revoke U.S. citizenship for foreign-born Americans.

U.S. Citizenship and Immigration Services, the agency within the Department of Homeland Security that’s responsible for legal immigration, sent experts to its offices around the country or reassigned staff members to look for possible cases where citizenship could be revoked. The goal was to supply between 100 and 200 potential cases per month to the Justice Department, which prosecutes them, NBC News reported.

Federal prosecutors in field offices across the country are working on the effort, the DOJ official said.

“The Department of Justice is laser-focused on rooting out criminal aliens defrauding the naturalization process,” a Justice Department spokesperson said. “Under the leadership of President Trump and Acting Attorney General Todd Blanche, the Department is pursuing the highest volume of denaturalization referrals in history. We are moving at warp speed to ensure fraudsters are held accountable and prosecuted to the fullest extent.”

Such cases of denaturalization have typically been very rare, involving people who concealed criminal histories or previous human rights violations during their application processes.

But throughout the four years of Trump’s first term, the administration filed a total of 102 such cases, according to the Justice Department.

The denaturalization push is part of an overall effort by the Trump administration to drastically curtail immigration and deliver on the president’s policy agenda. The push has included DHS sending scores of immigration enforcement officers into U.S. cities on deportation missions and purchasing mega warehouses to hold detainees.

It’s not clear why the Justice Department has singled out the roughly 300 foreign-born Americans. The New York Times first reported the tally.

The Justice Department had already told attorneys to focus on denaturalization cases, and it has offered possible case examples, from “individuals who pose a risk to national security” or have engaged in war crimes or torture, to people who have committed Medicaid or Medicare fraud or have otherwise defrauded the government.

Roughly 800,000 people become naturalized citizens every year, according to Homeland Security.