ROME (AP) — Pope Francis issued a major rebuke Tuesday to the Trump administration’s mass deportation of migrants, warning that the program to forcefully deport people purely because of their illegal status deprives them of their inherent dignity and “will end badly.”

Francis took the remarkable step of addressing the U.S. migrant crackdown in a letter to U.S. bishops who have criticized the expulsions as harming the most vulnerable.

History's first Latin American pope has long made caring for migrants a priority of his pontificate, demanding that countries welcome, protect, promote and integrate those fleeing conflicts, poverty and climate disasters. Francis has also said governments are expected to do so to the limits of their capacity.

In the letter, Francis said nations have the right to defend themselves and keep their communities safe from criminals.

“That said, the act of deporting people who in many cases have left their own land for reasons of extreme poverty, insecurity, exploitation, persecution or serious deterioration of the environment, damages the dignity of many men and women, and of entire families, and places them in a state of particular vulnerability and defenselessness,” he wrote.

Citing the biblical stories of migration, the people of Israel, the Book of Exodus and Jesus Christ’s own experience, Francis affirmed the right of people to seek shelter and safety in other lands and said he was concerned with what is going on in the United States.

“I have followed closely the major crisis that is taking place in the United States with the initiation of a program of mass deportations,” Francis wrote. “The rightly formed conscience cannot fail to make a critical judgment and express its disagreement with any measure that tacitly or explicitly identifies the illegal status of some migrants with criminality.”

It is one thing to develop a policy to regulate migration legally, it is another to expel people purely on the basis of their illegal status, he wrote.

“What is built on the basis of force, and not on the truth about the equal dignity of every human being, begins badly and will end badly,” he said.

White House press secretary Karoline Leavitt said last week that more than 8,000 people had been arrested in immigration enforcement actions since Trump took office Jan. 20. Some have been deported, others are being held in federal prisons while others are being held at the Guantanamo Bay Naval Base in Cuba.