– On paper, he’s a devoted U.S. citizen.

His official U.S. birth certificate shows he was delivered by a midwife in Brownsville, at the southern tip of Texas. He spent his life wearing American uniforms: three years as a private in the Army, then as a cadet in the Border Patrol and now as a state prison guard.

But when Juan, 40, applied to renew his U.S. passport this year, the government’s response floored him. In a letter, the State Department said it didn’t believe he was an American citizen.

As he would later learn, Juan is one of a growing number of people whose official birth records show they were born in the United States but who are now being denied passports — their citizenship suddenly thrown into question. The Trump administration is accusing hundreds, and possibly thousands, of Hispanics along the border of using fraudulent birth certificates since they were babies, and it is undertaking a widespread crackdown on their citizenship.

In a statement, the State Department said that it “has not changed policy or practice regarding the adjudication of passport applications,” adding that “the U.S.-Mexico border region happens to be an area of the country where there has been a significant incidence of citizenship fraud.”

But cases identified by the Washington Post and interviews with immigration attorneys suggest a dramatic shift in both passport issuance and immigration enforcement.

In some cases, passport applicants with official U.S. birth certificates are being jailed in immigration detention centers and entered into deportation proceedings. In others, they are stuck in Mexico, their passports suddenly revoked when they tried to re-enter the United States.

The government alleges that from the 1950s through the 1990s, some midwives and physicians along the Texas-Mexico border provided U.S. birth certificates to babies who were actually born in Mexico. In a series of federal court cases in the 1990s, several birth attendants admitted to providing fraudulent documents.

Based on those suspicions, the State Department began during President Barack Obama’s administration to deny passports to people who were delivered by midwives in Texas’ Rio Grande Valley.

The same midwives who provided fraudulent birth certificates also delivered thousands of babies legally in the United States. It has proved nearly impossible to distinguish between legitimate and illegitimate documents, all of them officially issued by the state of Texas decades ago.

A 2009 government settlement in a case litigated by the American Civil Liberties Union seemed like it had mostly put an end to the passport denials. Attorneys reported that the number of denials declined during the rest of the Obama administration, and the government settled promptly when people filed complaints after being denied passports.

But under President Donald Trump, the passport denials and revocations appear to be surging, becoming part of a broader interrogation into the citizenship of people who have lived, voted and worked in the United States for their entire lives.

Juan, who spoke on the condition that his last name not be used so that he wouldn’t be targeted by immigration enforcement, said he was infuriated by the government’s response. “I served my country. I fought for my country,” he said.