If Donald Trump keeps all his campaign promises, thousands of churches could disappear.

That’s according to Rev. Samuel Rodriguez, who heads the National Hispanic Christian Leadership Conference, an evangelical group with more than 40,000 affiliated congregations.

“The very viability of our churches—these are our church members,” he said. “You’re talking about shutting down churches. If you would ever deport 11, 12 million people, you would shut down so many Latino churches. And I mean so many in thousands, without any hyperbole.”

Advent—the four weeks before Christmas Day, when Christians traditionally light Advent candles in church and prepare to celebrate Christ’s birth—is supposed to be a season of hope, peace, and joyful anticipation. But for many Hispanic Christians, Advent this year comes with fear and deep uncertainty. That’s because less than a month after celebrating the birth of Jesus, a new man will come into their lives: Donald Trump. For churches and other faith communities with undocumented members, mass deportations mean empty pews and parentless kids.

It isn’t clear how many people Trump will deport and whether he will direct Immigration and Customs Enforcement (ICE) to target people who haven’t committed serious crimes. We just don’t know. So churches that minister to people without papers will spend this Christmas season hoping for the best and preparing for the worst.

And for many of these congregations, the specter of mass deportation isn’t theoretical. Rodriguez is the senior pastor of the New Season Christian Worship Center in Sacramento, California, and said his congregation includes many undocumented members. Though the church doesn’t keep tabs of its members’ legal status, on some Sundays it’s particularly noticeable. During Obama’s first term, Rodriguez said, he would sometimes notice dozens of members coming to church late, and all at once, on certain Sunday mornings.

“The ICE people would come in and sweep an entire neighborhood,” Rodriguez said, “so they would call each other and text each other and say, Don’t go out! Don’t go out!”

After the raids finished, people headed to church.

“We live that,” Rodriguez said.

After Obama changed his immigration enforcement priorities, there weren’t Sundays like that, he added. But the Trump administration could mean a reversal, or worse.

So Rodriguez’s group has been helping churches around the country prepare for changes that could gut them. They host weekly conference calls on preparing for the Trump presidency with megachurch pastors, pastoral associations, and denominational leaders. Interest in those conference calls was far greater than his group initially expected, he said.

“We do zero political analysis on the call,” he said. “It’s just pastors saying, Pastor Sam, what do we do next? Is he going to deport our people?”

One thing can pastors do: tell their members, from the pulpit, what to do if ICE shows up at their homes. Jessica Dominguez, an immigration attorney based in Studio City, California, works with churches in Rodriguez’s group to help pastors know what to say.

“My team and I consider it a calling to keep immigrant families informed about their rights, and work daily on purpose to keep families together,” she said in an email to The Daily Beast. “I consider it a blessing to work closely with pastors all over the nation to ensure that our community is informed about their rights.”

And some churches in Los Angeles are considering hosting undocumented immigrants facing deportation, on the assumption that ICE agents won’t enter churches to track them down. In the 1980s, many Christian churches protected Central American refugees from deportation as part of what was called the Sanctuary Movement. That movement still exists, and will likely be reinvigorated if Trump substantially increases deportations.

Alison Harrington, the pastor of Southside Presbyterian Church in Tucson, is involved with the movement, and said that in recent years, her church has housed two people to keep them from being deported—one for 28 days and another for 461 days. She said she knows of 16 people total who have hidden from immigration agents in churches since 2014. Her church helped launch the sanctuary movement when it first started back in the 1980s, and now works with churches prepared to shelter immigrants.

“It’s in our DNA as a congregation,” she said. “This is a fundamental aspect of what it means to be people of faith in the borderland.”

Before the election, Harrington said, she knew of 200 churches that had officially promised to shelter immigrants. After the election, an additional 250 pledged to be available if needed.

Harrington said her church also looks to help immigrant rights groups in other ways: by hosting meetings where groups teach immigrants about their legal rights, by providing free childcare at those meetings, and sometimes just by offering them office supplies.

“By offering a copier for people to make copies of training materials, you begin to build a relationship of trust,” she said. “And from that relationship, you’re able to do more radical work when the time comes.”

Sometimes that means going to the desert. The No More Deaths group, sponsored by the Tucson Unitarian Universalist Church, sends volunteers to areas with border crossings to give migrants food and water, and to provide first aid, in hopes of keeping people from dying while they try to cross the border. The group also does search-and-rescue projects if they learn about migrants who are lost from their groups and in danger. That’s according to Emrys Staton, who works with the group and is director of Pastoral Care and Justice Ministries for Phoenix’s Unitarian Universalist Congregation. The group, which also documents abuse of migrants by border patrol agents, has about 50 core members in Tucson and Phoenix, he added, and has worked with thousands of volunteers over the years.

“The election of Trump is taken very seriously as far as what that could mean for the border,” Staton said, “and No More Deaths has taken steps to start increasing our capacity to take a lot more volunteers, and ensure we have as much presence in the desert as possible.”

“At the core of it, we just believe that all humans have inherent worth and dignity, all people,” he added, “and we see that if people are moving across the planet, moving around—whether it’s for a better life or just because they want to move, whatever the reason is, they should be able to do that, and at least they shouldn’t be put through a situation where it’s extremely deadly, dangerous, and abusive.”

No More Deaths isn’t the only immigrant ministry gearing up for more demand in the Trump era. In Little Rock, Arkansas, Mosaic Church hosts a ministry that provides low-cost, pay-what-you-can immigration counseling to undocumented people. The pastor of that church, Mark DeYmaz, told The Daily Beast that the ministry currently works with 500 immigrants, and has seen a substantial increase in requests for help since Trump’s win. His church has many undocumented members, he added.

“Every now and then you just find out,” he said. “It’s not like we’re looking for it, but naturally if you’re living among people you learn some things sometimes.”

“They serve and they lead,” he added.

One member of DeYmaz’s church, who is undocumented, told The Daily Beast that attendees there worry about deportations under Trump but take comfort in their faith.

“For me, God’s got everything in control,” he said. “I’m trusting God. And it’s a little bit scary.”

“Hope is not placed in a man or a woman, whoever’s in the White House, whatever party is in power at any given moment,” DeYmaz added. “It’s not based on the rhetoric of the times or whatever, it’s rooted in your faith in God. And what we see in our people is that faith mitigates their fear.”

And churches don’t stop working when deportations happen. Rodriguez said his Sacramento congregation has protocols in place for when members get deported. If the deported person has a child, he said, his wife will go to the kid’s school to break the news. Then they will help the child find a relative or friend to stay with—preferably a U.S. citizen or legal resident. And people from the church contact the child every weekday for at least six months, he said, and help the child get to church. Children whose parents are deported become top targets for gang recruitment, Rodriguez added.

“They say, ‘Your mom and dad are not here. We’re your mom and dad. We’ll take care of you,’” he said. “And we want to prevent that. It’s a battle on all fronts.”

For the time being, Rodriguez said he hopes Trump will clarify his plans regarding deportations and commit to only removing dangerous criminals. In the meantime, his church will keep helping kids who lose their parents—as in the case of a 14-year-old girl whose mom was recently deported. That kind of loss challenges people’s faith, he added.

“This girl’s going, why did God permit this to happen?” he said. “This 14-year-old girl. So I’ve lived this out: What do we tell the 14-year-old girl? For us, it’s not like a story, someone else’s narrative; it’s part of who we are. The immigration struggle is part of who we are.”