The Trump administration is analyzing decades-old fingerprints in an unprecedented effort to rescind American citizenship from immigrants who may have lied or falsified information on their naturalization forms.

Revoking citizenship, a process known as denaturalization, has long been treated as a rare and relatively drastic measure by immigration authorities, reserved for foreigners who commit egregious crimes, acts of fraud, or pose a threat to national security.

But under a new policy memo issued by Francis Cissna, director of U.S. Citizenship and Immigration Services (USCIS), the agency is investigating thousands of old fingerprint records and files to determine whether foreigners made false or fraudulent statements in their attempts to obtain legal residency in the United States.

According to USCIS officials and documents reviewed by the Washington Post, Homeland Security investigators are digitizing fingerprints collected in the 1990s and comparing them to more recent prints provided by foreigners who apply for legal residency and American citizenship. If decades-old fingerprints gathered during a deportation match those of someone who did not disclose that deportation on their naturalization application or used a different name, that individual could be targeted by a new Los Angeles-based investigative division.

Violators will be referred to federal courts where they can be stripped of citizenship and potentially deported.

Cissna said the effort was crucial to upholding the integrity of the U.S. immigration system.

“The people who are going to be targeted by this — they know full well who they are because they were ordered removed under a different identity and they intentionally lied about it when they applied for citizenship later on,” Cissna said in a statement.

“It may be some time before we get to their case, but we’ll get to them,” he said, echoing comments made in an interview with the Associated Press, which first reported the plan.

According to the latest USCIS data, 2,536 naturalization cases have prompted an in-depth review so far, and of those, 95 cases have been referred to the Justice Department. Those numbers are expected to rise as additional fingerprints are digitized by ICE, but only an immigration judge has the authority to revoke citizenship.

USCIS officials said Cissna is acting on a 2016 report by the agency’s inspector general that found at least 858 instances of previously deported foreigners applying for citizenship under a different identity. The report said U.S. Immigration and Customs Enforcement (ICE) has 315,000 old fingerprint records being digitized and uploaded to the Homeland Security IDENT database.

According to Matthew Hoppock, an immigration attorney in Kansas who tracks such proceedings, the Justice Department has filed just 305 denaturalization cases since 1990, a sign of how sparingly the procedure has been used.

Several of those cases involved aging former Nazis, Hoppock said.