– Alarmed by President Donald Trump’s plans to crack down on immigration and expedite deportations, hundreds of churches, synagogues and mosques nationwide are considering the bold move to provide sanctuary to immigrants who are living in the U.S. illegally.

“When Trump was elected, it turned into an immediate priority situation,” said the Rev. Beth Brown, pastor of Lincoln Park Presbyterian Church, the first Chicago house of worship since the election to offer immigrants who are facing deportation a place to stay. There are now about two dozen in the Chicago area considering becoming part of the sanctuary movement.

Federal authorities say they’ll continue to avoid raiding hospitals, schools and houses of worship, but activists fear that sacred spaces could become targets and the movement will be forced underground.

Last week, a mother of four with two misdemeanor convictions sought sanctuary in the basement of a Denver church after authorities denied her request for a stay of deportation. How her case plays out could determine how congregations play a role going forward.

The idea of sanctuary goes back centuries. Greeks and Romans offered limited protections to criminals who sought shelter in temples. From the fourth to 17th centuries, English law granted immunity to fugitives as long as they were inside a church.

The more contemporary approach to sanctuary as a political movement in the U.S. first unfolded in the 1980s. Churches and synagogues opened their doors to immigrants fleeing civil wars in El Salvador and Guatemala.

In 1987, the U.S. Supreme Court upheld conspiracy convictions of several sanctuary ministers. But the same court also cleared the way for many of the Central American immigrants who were living in churches to seek asylum.

The movement resurfaced when deportations began to rise dramatically during the Bush and Obama administrations. In 2006, Elvira Arellano, a former maintenance worker at O’Hare International Airport, took refuge with her 7-year-old son inside Adalberto United Methodist Church in Chicago and became the face of the new sanctuary movement.

The targeted immigration enforcement tactics “go against the grain of what our faith traditions teach us,” said the Rev. Noel Andersen of the New York-based Church World Service, which tracks the sanctuary movement. “We believe that we … should respond to a higher law.”

Andersen said that 250 congregations nationwide signed up to help shield immigrants after raids in 2014.

Roundups in 2016 prompted more than 100 more places of worship to support the sanctuary movement. Now, 800 congregations have stepped up to provide relief, he said.