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 or acts of fraud, or pose a threat to national security.

But under a new policy memo issued by L. 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 with more recent prints provided by foreigners who apply for legal residency and U.S. 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 could 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 saidin a statement posted on Twitter.

“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 firstreported the plan.

According to the latest USCIS data, 2,536 naturalization cases have prompted in-depth reviews 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 a federal judge — not USCIS — 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.

Those prints can be compared with those already in the database. Foreigners who obtained American citizenship years ago and have been otherwise living quietly in the United States could be at risk of a knock at their doors.

A hypothetical example: A woman from the Philippines comes to the United States on a work visa in the 1980s and overstays. She is arrested and deported. A few years later, the woman marries an American citizen and returns. On her naturalization form, she deliberately does not disclose the previous deportation, and eventually earns U.S. citizenship. Twenty years later, when the fingerprints from her first deportation are digitized, the woman is notified she will be stripped of her citizenship for lying on her application forms.

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.

“There have been some years that the government didn’t file a single case,” he said. “Our hope is that [USCIS] will focus on people who actually committed fraud and deliberately made up new identities.”