NICK SCHIFRIN: Next week, when President Trump meets Chinese President Xi Jinping, much of the talk will be about trade.

But as he's done before when facing Trump pressure, Xi has launched a major crackdown on the country's Christians.

There are tens of millions of Christians in China, and earlier this month, Beijing arrested a prominent underground church pastor and more than 20 other clergy and parishioners.

In 2019, I traveled to China and saw firsthand how the faithful are often forced to pray behind closed doors.

NICK SCHIFRIN (voice-over): On the sixth floor of a Beijing apartment building, an unmarked door.

Inside a secret church for those prohibited from praying in public.

Xu Yonghai is the pastor of the Holy Love Fellowship and his congregation among China's most vulnerable Christians, critics of the Communist government.

His sanctuary, also his apartment and bedroom.

There was good reason for secrecy.

XU YONGHAI, Holy Love Fellowship (through translator): Since 2014, religious freedom has reduced.

On January 24, 2014, were taken to the police station.

Thirteen of us were detained as criminals for one month.

NICK SCHIFRIN (voice-over): By then, Xu had already been arrested three times.

But 2014 was the first time that authorities detained his entire parish.

XU YONGHAI (through translator): We were arrested because we defended the rights of other churches.

NICK SCHIFRIN (voice-over): Christian activists say the government has demolished thousands of unsanctioned churches.

There are some government approved ministries, but they have to display banners like this one that says implement the basic direction of the Communist Party's religious work.

Chinese President Xi Jinping has described minorities and their cultures and religions as threats to stability.

Most audaciously, in 2017, Beijing set up what activists call concentration camps for Muslim Uyghurs, crack down on their language and culture, and later move them into forced labor.

The U.S.

Accused Beijing of genocide.

The next year, Beijing banned Zion Church, one of the capital's largest house churches when pastors refused to install facial recognition cameras.

The church was forced to go mostly virtual.

Xu Yonghai told me his church and its parishioners were also under surveillance.

XU YONGHAI (through translator): They knew about our church, and the police had also come to our church.

But relatively speaking, were able to persist.

Our persistence is our main grace.

NICK SCHIFRIN (voice-over): For Zion Church instead of dying out, back in 2018, the congregation grew from 1,500 to more than 10,000 daily worshippers across 40 cities.

But today, facing domestic economic headwinds and once again pressure from a President Trump, the government has again cracked down on Christians and Zion Church's leader, Ezra Jing Mingli.

Earlier this month, Beijing rounded him up and detained more than 20 of his fellow parishioners.

NICK SCHIFRIN: I'm now joined by Grace Jin Drexel and Bill Drexel, the daughter and son in law of Zion Church founder Ezra Jin Mingri.

Thanks very much.

Welcome.

Grace Jen Drexel, let me start with you.

What happened when your father was arrested?

GRACE JIN DREXEL, Daughter of Ezra Jin Mingri: On October 9th, 10th and 11th, initially, up to 30 leaders of the church were taken away from nine different cities, including my father.

My father has severe diabetes and they are not allowing him to use his own medication and we're worried about his health.

NICK SCHIFRIN: How are you holding up?

GRACE JIN DREXEL: My mother and I and my two brothers, we're all in the U.S.

and we feel generally pretty safe that we are protected by our government's.

At the same time, to know that our loved ones are in China and we can't do anything and that they are unjustly detained just for their freedom of faith is really shocking to us.

NICK SCHIFRIN: Bill Drexel, of course, this is not the first time that Xi Jinping's Beijing has clamped down on Christians, nor is it the first time, in fact, that Xi Jinping has targeted the Zion Church.

So how is this part of a trend of Xi Jinping's China?

BILL DREXEL, Son-in-Law of Ezra Jin Mingri: Yeah, Xi Jinping's China has, from the beginning, really tried to push an ideological agenda.

And part of that has been tightening the screws on religious groups, not just Christians, but all religious groups across China.

Their first big push on this was around 2018, 2019, as you've researched, and now it seems like they're trying to finish what they started there or what was left unfinished.

NICK SCHIFRIN: And not just Christians against Uyghurs, against Muslims, against all kind of minority ethnic thought, religion and culture.

BILL DREXEL: Right.

What's the irony is his efforts to actually clamp down on Zion Church and many of the churches have really backfired because they took the physical meeting space of Zion Church.

They had to develop this kind of hybrid, online, offline, decentralized model that when COVID hit, actually really expanded dramatically.

NICK SCHIFRIN: Grace Jin, your father actually worked for a state sponsored church early on.

What was that like?

And why did he decide to launch an unsanctioned church?

GRACE JIN DREXEL: Many people in the U.S.

might think that a state sanctioned church, why don't you just join and just get legalized.

But what we don't really understand is that in China it means that you are in an ultimate control of this Communist -- Chinese Communist Party.

So for example, what kind of sermons you can preach on Sunday, how many people can be baptized?

Children are not allowed to be at churches because there's a law in China that says you can't proselytize to anyone under 18.

And so you ultimately realize that is a church that is in hostage.

It is not a free church.

NICK SCHIFRIN: Xi Jinping is traveling to South Korea next week.

He will meet with President Trump during that trip.

What's your message to President Trump ahead of that meeting?

BILL DREXEL: Our hope is that as a precondition, as a sign of goodwill, whatever it takes.

We would love for him to send a clear message to the Communist Party, to Xi Jinping, that taking prisoners of conscience as hostage in advance of these sorts of negotiations is not all right and that these prisoners need to be freed.

GRACE JIN DREXEL: Ultimately, I think this is beyond U.S.-China relations.

This is, I think, just a freedom of religion issue.

And I really again ask the global church to rise up and pray with us on asking my father and the 22 others to be released.

NICK SCHIFRIN: Grace Jin Drexel and Bill Drexel, thank you very much, both of you.

GRACE JIN DREXEL: Thank you so much.

BILL DREXEL: Thank you.